Here's a quick and dirty concept for a small slide-in inspired by the Scout Yoho but sized for the 4' 6" long bed of the Maverick. The camper structure itself is all right angles and sharp edges but the section forward of the sleeping area would be a rounded air deflector either made from solid foam or sheet metal or plastic over foam ribs. I even drew a little removable air dam that would clip to the bottom after the camper is in the bed to reduce air pressure under the cantilever sleeping area.
Interior width above the bed rails and overall camper height would be 6' 6", dropping to 6' 3" in both dimensions on the interior (1-1/2" walls, floors, and roof). The sleeping area over the cab accommodates a 75" x 54" full mattress with about 3' clearance above the top of the mattress. Total height above ground is about 9' plus anything that sticks up from the roof like vent/skylights. Interior layout is challenging since you only have a 6' 3" wide x 4' 3" long space to work with above the bed rails and only 4' 3" x 4' 3" inside the bed though the whole truck bed area has 6' 3" headroom.
The two layouts I am playing around with are 1) a love seat on the left running the full length of the space (so 4' 3") with a narrow folding table to eat "TV dinner" style (two people side by side) with the kitchenette opposite, or 2) single seats on either side of bed facing the middle with a folding table between them, and the kitchenette divided between two small units on either side of the door. If I did include a porta-potty or composting toilet it would have to be something that lives under a seat and gets pulled out or the seat lifted up to use occasionally.
Just a concept at this point, but feedback welcome!