I've seen small tear-drops on some smaller campsites, but not on Club sites.
Had a friend who converted a box trailer to a small caravan to use when he went to classic car shows. Fitted a bed down one side, and a kitchen come storage opposite, a couple of portholes for windows, a roof light and a big solar panel on the roof.
I would be looking to see if there is anywhere you can buy sheets of fibre glass, or sheets of aluminium, as this would make a lighter build than using sheet timber. Have a look a caravan breakers for maybe windows, skylights and any fittings you think you might need.
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