Pretend you're in Europe and take a shower maybe once a week. But everybody in the camper has to be in the "program". If you all have the same stank you won't notice it. Or heavy heavy applications of 3 day deodorant.
If you're determined to carry extra water I would use 5 gallon jugs behind the truck front seat, assuming you have a crew cab. Or, look at 20 gallon spray rigs for ATV use. They have a small 12volt pump and you should be able to engineer the wiring off your 4 pin truck connection. Or hook a hose to the tank drain. That's the biggest tank I would put on top of my camper.