Well, the few tubs I use (mostly for QT) have a UTH on each side for warm and cool temps controlled by separate thermostats. Granted, those t-stats are the ZooMed variety...but they work just fine for QT needs and are cheap enough to allow me to have 5. To raise ambient temps(in winter), I place a lamp about 8-12" above the top of the tub around the middle and use a 40 watt bulb.

With all the heck I've been through with these tubs: getting ventilation right to lower humidity, keeping the temp gradient right... I just really prefer my tanks! However, they are not practical given my limited space...so I'm building a rack that will use 90qt tubs for my adult BPs and I will put up with the endless tweaking to get it right for the extra space it will give me. Of course, my corn snakes and my younger BPs are staying in their nice stable tanks.