Here are some photos of framed trailer attached to the tow vehicle.

Shows the framing on the curb side. "Posts" are 1.5 x 1.5 common spruce bolted to the frame and then fastening an interior wall of 1/4" plywood to the inside of these posts.
The space between the posts will be filled with 2 layers of foil backed 3/4" foam insulation. Then covering the exterior with painted canvas.

Shows the framing and the adjustable wind deflector. In the finished version the solar panel would be recessed into the deflector.
The roof spars are 3/4" x 1.5" clear lumber glued and screwed to the side walls.
There are 2 layers of foil backed foam on the roof, foil is facing both inside (holds heat in), and outside (keeps the sun out).
Foam on the edges were rounded with a hot wire.
Yet to be installed are two 5' long grooved horizontal rails containing a rigid Coroplast panel that can be slid back when the hatch is up, creating a sheltered area.
The white trailer on the right is one I built last year. It turned out to be too big and heavy for my car. (68W x 73H x 108L, 830 lbs.)

Shows the future kitchen opening (the large foil area) and the hinged shelf. Kitchen area is too low for standing up, it's a crouch or sit-down area.

The crusty old-timer who is pushing this project. Must be fed regularly and takes numerous random timeouts. (Could be sports-events, or naps, or ... ...?).
Notice that the drop floor does not quite span the door opening. But by modifying the trailer frame (drilling a few holes and moving the draw-bar components forward about 5") the drop floor could span the entire door opening.
Too late to make the mod for this project -- I'll change it sometime next winter.