Yeah I understand, I'm not trying to bash your opinion or advice at all. Just trying to reinforce it.
6qt is really small, even for a baby pacman. I mean it's a lot easier to regulate the temps in a smaller bin like that, but I would only use that temporarily until you can work out a solution with your bigger tank that you have. The advice given from everybody should help you get the temperature back up so you can move him back into the other one. 14-20F, man that's hard to keep warm though. Can you get like an external heater for your room or some type of burners.
You should definitely do an insulated bin if it's that cold and you can't get some sort of heat appliance in the room you're keeping him in.