I have a small slide-out safe that's meant to go under a front seat and be screwed directly into the floorboard of the car. On a Mazda 2, is there any danger of screwing into a gas tank or something if I do this?
The gas tank is under the rear seat. There is an access panel for the fuel pump under the seat. The only way to really know is to figure out where you want to mount the accessory and get a good idea of where the fasteners will be. Find some reference points and measure things. Things like bolts that go all the way through or bumps in the sheet metal or some other protrusion make good reference points. Then get under the car and measure from your reference points to verify no issues. It sounds like you have not looked under the car yet. Get under there and make a quick inspection under the seat. You may find that the space is wide open. You should be able to make an initial inspection without jacking the car up. Or bring a mirror and flashlight out so you don't have to crawl around on the ground.