If you need a quick fix, just shine a 60 watt incandescent household bulb at the tub (not too close to melt the plastic). Obviously this is not a permanent solution, but it will be fine for a day or two.

Another option would be to get a couple of those instant hand warmers from the drug store and tape them to the outside of the tub

Also, I don't think so many binder clips are necessary. You probably don't need any of them.... I have kept a 500g snake in a crappy lock tub and they haven't been able to get out.