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When I get the camper built, it's going to have a gutter system to catch rain water off the roof. This water will be saved in 55-gallon plastic drums for bathing, washing, or gardening.
I've got an old tin-roofed farm house that's to be torn down because of tornado and termite damage. Taking the usable tin and building an open shed to park the camper under when it's not on the trailer. The camper is going to be like a 14' long slide-in camper that will be bolted or chained to the trailer, so it don't slide or fall off if the brakes get slammed. The shed will have a guttering system, too. Might bury a couple of 55-gallon drums and have a hidden supply of fresh water.