For short term use I have used a UTH unregulated on a 10 gallon tank.

I generally only do this for QT's and I place a 6qt locking tub inside the 10 gallon tank with a few layers of newspaper in the 6qt tub. Temps generally run in the low 90's in the tub. Only place about half the tub over the UTH. Not ideal, but works short term.