Other factors to consider....
If your foundation is pier & beam type (footings under the house) try to locate the safe above one to relieve the stress on the wood joist floor. If not, use plywood to span the space between two piers to support the weight. In most cases, you probably won't need it, if you can locate near a structural support like a beam or a vertical footing.
Safes like the common Liberty Centurion series weigh in around 100-200 lbs per square foot. Someone here can probably tell us what most residential floors are designed to hold (almost 598 lbs/sqft IIRC).
When you bolt your safe down, keep in mind the type of material you're anchoring to with the bolts. For wood, use at least 3/8" to 1/2" lag bolts and a large washer. The washer simply spreads any load on from the bolt head out so the head doesn't bear directly on the hole. For concrete, you can drill an oversized hole and fill 2/3rds with either new cement or epoxy compound and then drop the bolt in to let it all cure. Use the washers here too.
If you're in a humid area or have moisture issues around the house, cut a circle of neoprene rubber the same size as the washers. Use this between the washer and safe bottom to help seal out moisture from underneath.
Don't forget to level your safe. Using wood shims, like those for setting up door or window frames will work. Drive them under the safe until she levels out and then trim with a very sharp utility knife.
BillCA in CA (Unfortunately)