There is all that opportunity below the floor line.
What do you have planned for the fenders?
This was done for a pickup truck in 2013(!). But you have all that room to work with so you could do big spats. The construction is a metal C-shaped bracket and a piece of conveyor belting cut into a trapezoid. Fastened on two sides so it can flex on impact.
You'd want wide belting.
Six minute delta: The top is probably a simple construction. The most useful top is a trolley top. You have half of one already.
edit: One way to skin the cat: I estimate a length of 21ft (to make the math easy). Acquire an arcylic tube 6" x 7' and cut it into three 120 degree sections epoxy those onto a flat metal truss. Such that the acrylic is a stressed member and the metal is sized to make a 21ft ridge/skylight. (The truss doesn't hold the edges up, it holds them apart)