Well, I suppose you could go to the hardware store and buy some sheets of 2" thick owens corning pink board...the styrofoam stuff. Cut it to length of all the sides, double it up, and you'd have a decent box to surround the sides of the tank. That would slow heat exchange. I'm sure you could tank the top off the tank and lay some doubled-up insulboard over it to keep the heat in that way. It's a bit involved and you'd need extra space to store the pieces, but like you said Don, storing all that would be ridiculous. It would work to hold the heat in for a little while but it wouldn't matter over the course of a couple days though. Eventually the temp is going to drop without some outside influence.