Insulating outdoor caged water holding tank

Foam insulating sheets, as thick as you can find, probably 4 or 6 inch with an electrical heating element inside if it gets really cold. Use multiple 2 inch sheets if you cannot find thick stuff. Do not use fiberglass insulation, it's worthless if it gets wet. Have a removable insulated lid to provide access to the tank.

I'd probably wrap the whole thing protective material like 3/8 painted outdoor plywood