Whatever you do, bolt it down. Having a safe that isn't secured doesn't do you much good as any would be thieves will just carry or dolly your safe out and work on getting it open on thier own time.
A friend of mine recently built a new unattached garage next to his house. When the floor was poured he poured a thicker section, 3'x3'x12". He anchored his safe down with 6" long bolts.
Century Arms AR-15A2, 5.56
1946 Mosin-Nagant M44, 7.62x54R
1978 YUGO SKS, 7.62x39
NEF Protector Pump, 12 gauge
Savage Model 64, .22LR
NEF Pardner Tracker II, 12 gauge
Rock Island Armory 1911A1, .45 ACP
Remington 870 'Express Magnum' 12 gauge
Bersa Thunder .380