One really should not store a safe in the basement - especially if leaky walls/floor in heavy rains. meaning if this past June you had any water on the floor, it's a bad idea to have a safe down there.
As for the garage--yes it can be a problem as temperature changes can cause condensation. EG condensation on the gun barrel. Especially if you occasionally fire up a heater to work on your vehicle. Think of condensation on windows with temperature differences (10 outside and 60 inside), same thing on metal.
Most gun safes are just security from smash and grabs. Side entry is where the pros go for, meaning they use a metal cutting saw and saw right through the side VS the myth of going through the door. As for a "security" cabinet, well that is just so the kids can not get their hands on the guns with out you knowing about it. These an amatuer can get into in 10 seconds.
Recently I noticed many gan safes going to a 1/2 hr rating VS the 1 hr which was the standard. Realize that 1/2 hr or 1 or 2 hrs rating is how long the temp inside getting to 450 degrees--the finish on the guns is shot way before that point. 452 degrees if I recall correctly is when paper (legal documents, etc) catches fire.
Now the serious gun enthusist buys a gun vault. This is the real deal.
But they cost a LOT of $ too. But if you have $250k in guns, what's another $6-12K for a vault?
Also for consideration is insurance premiums. Certain rated vaults you will get a good discount on your gun insurance from the Ins CO. I've heard a few Ins COs also give a lessor discount for having a "safe", as less risk of theft during a burglary.
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God, help me be the man that my dog thinks that I am.