Whatever you do, don't cut up an old VW bus to graft onto the roof. Sailboats have an upper deck that has been evolved for 100s of years to be useful. Stove in the bottom and they get pretty cheap (one would think
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I wound up in a 35ft R-license park model trailer. There's a lot to be said for hiring the tow vehicle.
That said though, here's my scenario. 60-pass bus with the top half cut off the back emergency door and a wall with full door 4-5 feet ahead. Left rear corner is a (55-gallon drum batch process) composting toilet. Right rear corner is a 7ft tall wood alcohol still.
The front bumper is moved forward 2ft and there is a wood chipper clutched off the front of the engine (and an electric winch). There is a 4" round duct from the chipper to a bin on the rear roof to feed the still.