I live in Seattle, Washington and have the world's tiniest bathtub. It sucks. So I'm attempting to design and build (ha! I mean "have built") a tiled soaking tub that will be on an outside ground level wall. It gets pretty chilly here and I'd hate to fill up an ice cold tiled tub with hot water only to have it cool quickly because of the cold tile. So I've read about people utilizing radiant heat under tiled shower floors and thought it would be a great idea for the bottom of the tiled tub and maybe even up the back (the part you lean against). I called Sun Touch to ask about that sort of installation and they disavowed any knowledge of anyone doing that because it would be an application that would void the product warranty. I may have been hearing things, but I think I may have heard a nudge, nudge, wink, wink in there somewhere, too. So, has anyone got any ideas about this or know of someone who has done this? Also, how can I efficiently insulate the tub structure from the ground? Styrofoam, closed cell foam, icynene, etc? Thanks!