Okay- I'm up to speed here
There is another option to plastic and fish tanks and they are called reptile cages. Check this out: http://www.reptilebasics.com/2x3-Cag...h-p-16286.html This is a reptile cage from a very well respected business. For the cold temps in your apt, I would recommend heating with a radiant heat panel (RHP). Radiant heat panels not only provide the snakes with the belly warmth that they need, but RHP's also help to raise the ambient temps which it sounds like you need in your situation. You would need a thermostat to control the RHP. Because this is a reptile cage, only the front door is see-through, adding to the comfort and security of the snake. RHP's do not zap humidity as with lights over a tank.
Really check out these cages specifically designed for reptiles. I have tubs in a rack and I also have 6 of these cages. I am slowly moving all of my snakes into the cages. These cages are easier to clean because the snakes have space to get out of their own feces. This cage also provides exercise since they cruise around at night. Frankly, I'm feeling really bad about keeping snakes in tubs these days....