Your guidance is requested.

I would like to purchase a CHEAP 870 police shotgun to use as my truck SHTF gun (I don't have a CCW).  I want to replace the stock with an over-folder stock to reduce the length while stored.  I plan to also get a police shotgun lock to attach the shotgun to the truck behind the seat.

Now, I don't expect any type of long range shooting, basically a short-range self-defense gun to get me home.  I want it CHEAP because it will remain in the truck except when I'm home.  

How good an idea to purchase a 870 police model in "good" condition for what I plan to use it for?

How short can I legally shorten the barrel without obtaining a permit?

What overfolder would you recommend?  

What kind of optics (if any) would you recommend?  Or would special sights be preferable?

Any assistance is greatly appreciated.

-KW

Don't get the folding stock!! Top folding stocks are the worst thing you can put on a shotgun, if it's going behind your truck seat length shouldn't be an issues.

Look on the EE for cheap police trade-ins. I bought a used Police Magnum 870 off of auctionarms.com for about $200. That is the 870 I baby. My junker/trunk gun 870 came from a local sporting goods store. It was an older Wingmaster with no vent rib. I walked out the door with it for $125. I took it to a gunsmith and had the barrel shortened from 29" to 18". That is the shortest legal length you can go without it becoming an NFA firearm. I then bought a used factory Remington top-folding stock for it. It was rather expensive but completely worth it. It makes it very compact, and the fact that it is a factory Remington stock means its high quality with tough steel and a pistol grip that is so damn ergonomical on the 870.  My advice to you is find an older 870 and customize.  

I took Mikes advice and bought the 5077.  Couldn't be happier with the purchase.  It's perfect for home defence and really doesn't need any modifications at all.  Bought mine for $292 shipped to my FFL.

First the gun options:
Buy a used Police model.  Check on the High Road's Rifles and Shotguns for sale forum.  A member is selling good Police models there:  http://www.thehighroad.org/showthread.php?s=&threadid=98782

Buy a Remington Express HD or the HD model with the factory extension.  Price is right, and you get a NEW gun cheap.  While not as well finished or smooth as a Police model, it'll last as long.

Haunt the gun shops and pawn shops looking for a good 870 Wingmaster or Express.  Often you can pick up good guns cheaper than any of the above, and if it's a Wingmaster model it's the same gun as the Police model, with a commercial-grade bright finish.

Barrel length. Minimum barrel length is 18" under FEDERAL law.  Some states or local areas may differ.

Folding stock.  Folding stocks are primarily special-use items for SWAT teams, who actually use the shotgun as a TOOL to force open doors, not as a weapon.
Folders are most often a "Hollywood" thing used in the movies, and by people who aren't familiar with shotguns.

They LOOK like a great idea, and appear to be ideal for a short defense gun.
In fact, MOST people who actually experiment with the folder in realistic shooting courses quickly find out that the folder is one of those "good ideas" that just don't pan out in the "real world".

Recoil from a shotgun loaded with buckshot is HEAVY, and the folder actively punishes the shooter.
The metal or hard plastic is particularly bad on the face.

Firing the shotgun with the stock folded quickly turns up the "dirty little secret" of the pistol grip or folder stock:  In real defense/combat shooting, not just playing around on a range, accuracy and speed DROP with the pistol grip stock.

Due to the recoil problems and the better control, speed, and accuracy, MOST people quickly go back to a full butt stock on the gun simply because they HIT better with it.

Optics:  Optics on a close range defense gun are actually an impediment instead of an aid.
Standard telescopes are useless on a defense shotgun loaded with buckshot, since the shotgun is at absolute best a 50 yard gun, and most experts say 35-40 yards.

Electronic sights have the problem of the battery or sight failing when you need it.  This is going to be a real hazard in a vehicle gun which gets less maintenance.

Any honest shooting comparison quickly proves that a good shotgunner is actually faster without optical sights, and it's the shotguns SPEED that makes it so effective as a defense gun.

On a defense gun you're better off with your choice of plain bead, or some type of rifle sights.

My suggestion is, buy a shotgun and plenty of ammo.  SHOOT the gun in as real a HD situation as you can, THEN decide what accessories you want on it.

Remember, about the perfect HD shotgun is an 18" barreled shotgun with a full stock and NO options.
EVERYTHING you add has a trade-off.  
The trade-off is lesser speed getting shot on target.

You have to to an HONEST cost-benefit analysis on each option: What are you getting that makes it worth the loss in speed?

Want an electronic sight?  Under what circumstances is it going to be a benefit on a 50 yard gun?
It's going to take TIME to turn the sight on, (hoping the sight and battery are OK), and get it on target.
Is whatever benefit you may gain worth the loss in speed and reliability of the sight?

Buy a gun, shoot the gun A LOT, then decide waht you really NEED instead what looks cool or seems a good idea.

Thanks all for the advice.

I am somewhat of an experienced novice, if that makes sense.  A better description is probably a novice with some experience.  While a Marine on embassy duty we were armed with .357's and 870P shotguns with folding stock.  I know what you mean about the metal folder punishing you.  My thought was to accept the added difficulty with the recoil to allow for better concealment inside my truck.  Still contemplating that one.  

A stock is definitely necessary though.  Others experience may allow them to fire well without the stock/stock folded, but I found it only good for the first shot, with follow-up difficult.  We actually had one of our Marines fire the shotgun from the hip with the shotgun held too far to the rear.  The recoil broke his wrist.

My gut instinct was the same as yours Faris in regards to the optics.  I have a Mossy 590 for a house gun, and it has a bead sight.  I was wondering if there was some sort of sight that worked well that I was unaware of.

With the role of the 870 to be a truck gun, I'm still looking to purchase a CHEAP used police gun.  If the finish is scratched or worn, it's no big deal to me.

Thanks again for the advice.  Please don't hesitate to send more info my way.

-KW

Unfortunately the words "Police gun" and "cheap" don't go together much.

Police guns bring fair prices even in heavily used condition.

The up side is, most Police issue guns are carried in patrol cars a lot, and shot very little.
Since the 870 is a tank, even a worn gun is in quite usable shape, and everyone KNOWS it, thus the high prices.

You can check around, but finding a used Police model in any condition is a matter of luck, and just happening to find someone who has a batch.

Other than the above link to the guy selling on the High Road, you might try Kentucky Imports and CDNN.  Both of these often have used Police guns and parts.

For sights, you have a choice of bead, standard Remington factory rifle sights, and any of the ghost ring (peep) sights.

Adding different sights later is tougher.  The Remington factory brazes factory sights on, and these don't come off very easy.

Your best bet is to try to buy a gun with your choice already on the barrel.
The guy on the High Road apparently has a source of Police guns, and usually has a either bead or factory rifle sighted guns.

If you really want a folder, the factory is about the most expensive, and hard to find.  
There are several newer types around that look pretty good, and are a lot stronger than most of the older versions.

There's two diferent guys on the EE selling used police trade-ins right now. Not exactly cheap when you factor in shipping and FFL.
I was looking for a good used 870 also and visited a few pawn shops this past weekend. The prices they wanted were absolutely rediculous. I could get a new one for what they wanted. Their attitude was "someone will come along and buy it". Maybe, but not me.
I just went and bought the 5077 HD model. Nice gun.

I bought the 5077 and I really like it so far.  What is the main differences between the police issue and the 5077 besides the finish?

The Express is a "bottom of the line" budget gun, intended to sell at a price near that of the much cheaper to make cast aluminum and stamped Mossberg and Winchester.

Since the 870 still uses a forged and milled steel receiver and heavy duty fabricated parts, costs had to be cut, and what got cut was finish, and the addition of some plastic and MIM parts.

Here's the actual differences:

The Express Home Defense Model has:
A plastic trigger group.
The Express MAY still have the lockable safety button.
The dimples in the mag tube and the new style magazine retention system.
A rougher finish inside and outside.
A rougher blue job.
A less polished bore.
A two piece barrel. (not 100% sure about this)
Hardwood or synthetic stock, with a sporting-length fore end.
An 18", cylinder bore barrel, with a bead sight.
Some Metal Injection Molded (MIM) parts, like the extractor.
(The Epress fitted with the factory extension does not have the "dimples in the mag tube)

The 870 Police has:
An aluminum trigger group.
NO lockable safety.
The old style magazine retention system.
A much smoother finish inside and out.
A military-grade parkerized finish.
A polished bore.
A one piece barrel.
Walnut or synthetic stock, with a short police-length fore end.
Choices in different stocks, including Speed-feed, and others.
18" to 20" improved cylinder barrel, with a wide choice in sights, including rifle, ghost ring, and luminous.
Heavy-duty magazine spring.
Heavy-duty trigger-sear spring.
Sling swivel mounts.
No use of MIM parts, the extractor is milled.

Thanks for the knowlege guys.  

I really like the dull look and the synthetic stock.  Since I bought the 5077 model, I don't need the extention so that's not a concern for me.  The only thing that I may do is change out the trigger group someday.  I think for home defense, 5077 is hard to beat.

Thanks again for all the knowlege.  I've learned a lot and feel very good about my choice.

I would not reccomend buying anything repeat anything used by police.  Any abuse you can think of and many you cant think of are inflicted on the equipment they use.  

Quoted: I would not reccomend buying anything repeat anything used by police.  Any abuse you can think of and many you cant think of are inflicted on the equipment they use.

Nonsense. I bought a used 870Police from the police trade-in and it runs fine. A lot of the guns were stored in the trunk more often and used/abused.