Title says it all.

I have a choate 10 rd. extension on my 1200 and it has always served me well.

are they aluminum or steel?

Quoted: are they aluminum or steel?

they are steel

I really like the Winchester factory extended magazine because of the clean, solid tube verses the usual screwed on two or three shot adaptor. It just makes sense that a solid all of the way mag tube will be better, you get rid of a potential problem area, the spot where the extended mag screws on, and it just looks a lot better. I very much prefer the Remington 870 shotgun and would like to see a factory correct solid length magazine tube for an 18" barrel shotgun. Also, I would bet that it would be awesome if the Remington 870 had the same type of "gas pump assist" (I forget what it is officially called) that the Winchester 1300 has. I really like that gas assist, if basically racks the shotgun right after your shot.

How hard is a tube swap.  I see lots of parts on Gunbroker.  They sell defenders minus the receiver.  Is it possible to stick the defender tube on my receiver, then just put the 18 barrel on.  I guess I could always buy a parts gun.  I plan to keep my 1300 for a while it gets a ton of hunting use.