Any kind of floor. Currently its concrete, but I have to build it up with something about 2" so it clears a water line. I was planning on using drywall to raise it up so it can provide insulation too. I can put whatever I want on top of that.
I am really starting to like the idea of putting down some white plastic laminate. That should be slippery. If its not good enough, I could also grease it with some silicone grease. That would be cheaper than steel.
The other thing I am trying to decide is whether to get a 30" wide safe that will fit beside that water pipe, or a 39" that would hang over the water pipe. I am a little worried about not having easy access to the pipe should it develop a leak. It's a 1/2" supply line to a spigot on the other side of the wall. It comes out of the slab right where I need to move the safe. I am planning on putting a 90deg angle right where it comes out of the slab an run it along the floor to a new location. That is why I need to elevate the floor a couple inches, to make room for that.