Looking for a place to post my latest project, and I ran across this thread. Go figure.
I share the contempt posted earlier for the Sentry, and similar "safes". Drywall resists fire by releasing H2O which is contained within the gypsum.
For added security, I can remove the bolts from the weapons and post a notice on the door –– what thief would take the trouble to pry it? [ I've got the bolts in my big safe –– not that little peanut safe in the pic.]
My box is a "Klein", a HomeDepot brand. It has knockouts for power, and the rack is just a shelf I had in the shop. It holds 25-30 easy, but is only 48" tall ( a squeeze for a Swedish Mauser).
I still need some Chinese floor mat on the walls to insulate it. It will have a small fan-forced ceramic heater inside, like my Liberty L-25. I also put in a can of silica gel.
[ETA: Yes, there may be a Fudd gun or two in there!]