If you hook up flexwatt to a good thermostat, that would be a good tub UTH.
An adult could live in a 32q tub easily. Much more of a space saver!
You can look up flexwatt on reptilebasics.com as well. Rich will wire it for you and everything. 3-5 dollars a tape usually.
You might want to invest in some foil tape to attach it to the tub (or preferably the surface your putting the tub on) to hold it in place and transfer heat still. Avoid sticking UTHs to class or tubs, as usually the UTH is ruined and can't be reused in a new enclosure. :]