I run set ups in cool rooms all the time. Typically below 68ºF in the winter. I'd disagree that a tub is the way to go they are about the worst for insulation out there. It is easy to prove see how quickly the temperature changes when you hold your hand behind a lid. Almost instantly. Glass has great thermal mass that is a start. The best would be custom designed enclosures.

In absence of that I'd stay with the glass tank the troubles are two fold heat rises and the top is open. The other problem is the volume of air inside is in height. To be honest insulation might work but I'd suggest a bigger change that can make a big difference it will take a bit of fiddling with but it should resolve the issue.

Side turning the tank will help hold heat a bit and insulation will add to that. The problem is the CHE will have to go. I'd replace it with a flourscent light inside the enclosure it will add ambient temps in a huge way. Fixing it is hard and complex but I have used hot melt glue and magnets (1 inch by 1/8 rare earth ones and six of them if you can find a supplier. They have a 20 lbs pull apart each so six is 120 lbs total my snake after six months has never moved it yet.)

http://ball-pythons.net/forums/showt...arium-Solution

The real example is this exact set up is this morning in a room that is 63ºF the UTH is holding the hot hide at 90º and the surface cool end in at 79º and ambient air is 83º. It works if you have the time and effort to set it up.