Personally, I would avoid the vinyl tiles. Unglazed stone tiles can be found at most home renovation stores and are better at holding the heat. Besides vinyl giving off gases, typically the backside is prepared with adhesives that can also give off fumes that could be detrimental to your reptile.
I've got an 8x8" UTH with the 3/8" thick tiles from Home Depot (3.99 for a package of 9 4" tiles made from travertine). The UTH is on the left side of the tank and partially under both the humid and warm hides: