That why I ened up using paper towels for substrate, cleaning ease I can clean and disinfect a tub throw it around to dry it in like 5 mins paper towels are great bedding cleaning supply and if you have any hatchlings to tube is their fav hide ever. There is also a paper roll product ment just for lining tubs and its avlibile in bulk
the heat on the plastic is why I'm using side heat,for now I have already seen warping when I put the Uth on the lid of they empty tub below. It maybe the hefty brand being made cheaper that others I don't know but the belly heat is a concern for me too. Your not supposed to reuse or heat up bottled water cause it releases something out of the plastic so I imagine a Uth does the same to a plastic tub