I would replace the water bowl with one that is wider at the base than the top. My BP's would have the one you're using dumped in minutes.
Glass is an awful insulator. If you still can't keep the temps where you want them, cut some cardboard pieces so they are big enough to cover both long sides and one short side, and attach them to the outside of the tank. Alternatively you could wrap the tank in a blanket. It won't look great but it will work.