With that age of a TC and the fact that they were trying to save weight to fit on smaller trucks then you probably do not have a battery on board. My 1992 camper did not have space either as back then they thought you would tie it into the truck battery. If that is the case then the power supply is more then likely not a battery charger but a 12V converter (be careful if it is just a converter as it will fry your battery because it will not shut off from charging).
The ice box would also point to the weight saving idea as a fridge would have been more weight and cost.