Greetings & Welcome!
I would build a foamie camper for your truck. Extremely lightweight, yet extremely sturdy. With your bed over the cab, you’d have plenty of room in the bed area for a kitchen, wet bath, and seating/dining area.
Now you’ll have a large roof for solar, and sturdy walls, hopefully with lots of windows, surrounding you. The foamie construction means it’s already well insulated, so it should be easy to heat/cool. I wouldn’t put in any roof vents, and choose wall vents instead. With a couple being low, and a couple being high, you can take advantage of fan free cooling during the warmer parts of the year, because the heat will automatically exit out of the higher vents while drawing in cooler air through the lower vents. The vents need to open/close, and I would put reversible fans in for the upper vents. Then you’ll have great rain proof ventilation with no worries of roof leaks ever because you will have no holes in your roof.
You can make the camper very aero dynamic so it will have a minimal impact on your MPG. Use the same foamie method inside for all your cabinets, bathroom & closet walls, drawers, etc. Lighter weight means better MPG.
I’ve built a few for people, and they’re cheap & easy, yet extremely robust & sturdy. If desired, you can even even extend them beyond the truck bed in the back, and/or wider than the truck bed above the the truck bed. This will allow you to sleep width wise over the cab.
With an intelligent floor plan, you can have a camper that will be the best of all worlds, and last longer than a lifetime. You will also be able to move it to a new truck if the need arises, or sit it on the ground at a campsite or the repair shop if your truck needs repairs.
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