Heat a tub is more difficult in some ways than a tank. If you have good ambients it is easy if you don't? It is very very hard there is no good and safe option to do so with a tub. I would suggest a plastic enclosure over a tub in my experience tubs are the most difficult, racks next, tanks then custom enclosures the easiest, my house is cool at best (to me 69ºF is normal so below that most of the time.) I like vision enclosures because they are easy to clean (round corners) but there are a whole range of slab built types out there as well.