Honestly, I haven't actually made these yet, but the cages they're going in are built, and I've pretty much got the details worked out. I'm going to place the tiles back-to-back, with the smooth side out (so they're easy to clean), and the heat tape in between. There really won't be any space between them, except to accommodate a bead of silicone around the edges for sealing, and a blob of epoxy to prevent any issues with the cord getting tugged on. Keep in mind that this is only for those who are familiar with wiring/soldering/insulating their own heat tape. Maybe not the best project for the first-timer. You could kill your snake or even burn your house down if it isn't done correctly, but you asked about the heat tape specifically. It could be easier/safer to do as Nanci suggested and just use an UTH (maybe without sticking it down - they're really not moveable). Oh, also, make sure that wood is sealed well!