[aerohead]

The ability to telescope up and down as shown is limiting all the leading edge radii as well as longitudinal radii necessary for a drag minimum.
I'd guess that the camper shell has about Cd 0.7.Like a early 1970s JEEP.
*You need a minimum of 80mm radius on the leading edges just to maintain attached flow onto the shell.
*Something like a 'NOSECONE' brand style fairing shaped nose would be ideal.
*An 80mm radius down the top sides won't cut the Cd but it will really help with crosswind stability as far as rolling moments go.
----------------------------------------------------------------------------All the things necessary to cut drag really amplify the difficulty of fabrication.
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An upside down aluminum boat,nose first,mounted above the camper might help.