My safe is in the basement. I have one of those rechargeable dehumidifiers and a golden rod. Humidity has never been a problem. I was also concerned about water in the basement, even though I’ve never had any water. I have my safe raised on 3 pieces of 2 x 6. I figure 4.5” of water I’d the whole basement would be a Lot.
Another thought / recommendation: I have it against a wall and bolted to the floor. When I bolted it down, I drilled all the way thru the floor. The anchor bolts catch just fine, but if I ever need to move the safe, I can just drive the bolts down thru the floor. (That’s the way many machines are mounted to the floor of factories).