I intend to leave mine easily accessible too. When I tore up the floor I could tell nobody had opened that area up since the bus left the factory in Georgia in 1995. I could tell this because the hole was covered with an approximately 6 inch square steel patch, originally painted aluminum grey, but by the time I saw it now slightly rusty. Underneath the patch was just the ugly green MLV flooring, intact, over a big hole in the plywood. If anyone needed access to the tank, they would have cut the vinyl.
Since nothing has been done in the fuel tank since 1995, I think it would be best if I planned ahead and kept things as simple as possible. Just my 2 cents worth. Interesting thread, thanks to all the posters.