I bought my Ft. Knox before I moved out here and had a concrete pad in the basement of my townhouse to place it inside.  I moved out here a few years back and thought 'I'll just get someone to move it into my basement'.  The problem I found is that a structural engineer said my floating floor in the basement wasn't designed to hold 200+ lb/sq ft dead weight w/o sinking some concrete piers for support.  (the Ft. Knox is 1500 LBS dry)

So, my question is whether anyone has their safe in their garage w/o AC or heat and how is that working out?  I recognize the other than environmental issues making it easier to break into or steal in one piece, but in my situation I either use the Ft Knox that I already have and set it up in the garage OR buy some smaller RSCs (plural) to store my gear inside the house and unload the Ft. Knox.

Stick it in the garage. I have no issues with the ones we have. No matter where they are located, inside or out. It doesn't get humid enough to worry about guns not in a safe.

I guess I'm mostly concerned with the wild temp swings and the effect on wood stocks.  I have a goldenrod that I can use to help, but my garage can get really warm in the summer and cold in the winter.  I guess the goldenrod and possibly a low wattage light bulb on to keep the interior above freezing inside the safe in the winter, but it won't be warm by any stretch of the imagination.  I could possibly put up insulation between the bare studs in the garage, but I don't think that would have much impact on the temp swings.

Get a smaller safe for inside? Store the wood stock stuff in there?

Or insulate the garage and heat it. Just thoughts.

No issues as long as they stay dry.

This is the first I heard that the basement floor couldn't support a gun safe.  I got my Ft. Knox sitting in my basement fully loaded for the past five years with no issue.  I have an unfinished basement, so I'm in direct contact with the floor. Only thing I did was put some hockey pucks between the safe and the concrete.  If the concrete in the basement couldn't support the weight of the safe, why would the garage be any different?  Hardest part I had getting the safe in the basement was getting down the stairs.  I suggest getting a second opinion from another engineer.

My problem is that my basement has a floating floor as opposed to a concrete slab.  The structural engineer I had in for another issue said that it wouldn't be a good idea to put the 1500 lb safe on the floating floor w/o sinking some piers.  The only concrete slab that I have is in the garage.

You're over thinking / worrying this. I have no heat in the garage, just insulated. To Date wood furniture in plastic bins have suffered no issues from weather swings, considering they've been in the shop along with lots (ok a few) uppers, bbls etc for 10 years or so. Not to mention my reloading presses and components.
. A quality safe not only protects against fire (for a period of time) but some moisture too. You could install some felt weather stripping along the door frame.
You could also use that crystal kitty litter which is the same stuff dehumidifier packets are made with.

My good friend has a full size pool table in his basement with a floating floor (made of wood), and he hasn't had any problems.  As a matter of fact he just had his house flooded (water supply line to fridge) and the wood was fine.

Thanks for the input.  I'll get a 2nd opinion on what my floor will support w/o sinking piers as I'd rather have my safe inside than in the garage.  Barring that, it seems that placing it in the garage isn't as much of a problem as I thought it would be with regards to potential damage to the contents.  Especially with the low humidity out here.

What size and series floor joists do you have?

I'm not really sure.  I'll have to get into the crawl space and check, but I won't be able to do that for a few days.