Decoy safe is an awesome idea, instead of cash i would be more inclined to booby trap. Taser comes to mind, you can get a triple shot one now.
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The only advice i can add is that you may want to rethink any extra money for fire resistance. I installed one in my buddy's garage ($3000 variety). He had me bolt it to the cement pad and part of the foundation wall. I called the manufacturer in order to find the best way to find the pre-drilled holes in the safe's outside wall. The dude on the phone didn't have a frigin' clue so we just started pulling things apart. We found that the fire resistance was accomplished with half inch drywall, three layers thick with felt glued onto the top layer. Drywall is great for fire protection but you should not pay extra when you could buy a cheaper safe and then design and build a cabinet utilizing the same drywall for comparatively no money and a much lighter safe. If you pay massive money for a fire proof safe be sure that fire resistance is at least done with
refractory cement it is a denser product and is superior to drywall . DIY options also include "rock wool" and "kiln bricks". As far as keeping things climate controlled, the first thing you want to do is insulate the rest of your garage (with the money you saved not buying a crazy heavy safe) also dry wall over the insulation to further prevent the hazard of fire to your house and your weapons. Insulate your garage door as well, as best you can (foil faced 1.5 inch hard foam, spray adhered to the inside of the door) . Then get yourself some desiccant packs big versions of what you find in your new shoes and put those in the safes. Check on your weapons at least monthly to make sure they don't get too dry.
p.s. fire caulk any penetrations through your safe.