I made one of those.I wired up my new topper with three 12v outlets, lights and a deep cycle boat battery in box w/ charger and volt meter to run an air conditioner made from a ice chest+aquarium pump+heater core+12v fan
I wasn't really happy with it.
It drips a lot of condensation and eats ice way faster than I'd imagined.
I hope yours works better. Let us know the results.