What you see in the picture, front to back:
a "maxx" air fan and housing over the bedroom. Max disturbed air, that is!
Maxxair Vent Corporation
I can take the fan out of it, and build a bubble housing that will have a lower profile and much less drag. A wintertime project.
There is a smaller fan over the shower and a skylight that are much cleaner.
Next is that huge AC unit. I was thinking of a lightweight razorback cover transitioning from the trailing edge of the upper roof, over the AC unit, all the way to the trailing edge. I'd ventilate it for the fridge, AC, and that last Maxxair cover over the kitchen vent.
That would smooth things out considerably, but as with the boat tail it would have to be stout to withstand the gusts.
I called my wood supplier and got some prices. The least expensive 4MM marine ply was hydrotek, at $28 per sheet. 18.5 pounds per sheet. Okoume was down to 13.5 pounds but right around $60 per sheet.
That is too much.
If I build an aluminum frame, will 4 or 6 MM Coroplast hold up? Has anybody glued it, or epoxy?
On the truck bed/running board:
I will be building a fillet fairing out of wood for the crash there at the front of the box.
Imagine a triangle with the point almost to the back edge of the door inboard, angled out to eventually match the box profile.
I started covering the running boards with wood today. They are not ideal aerodynamically in any way, but they are not going to be changed.
It will be very easy for me to put a 3/4 belly pan on it and tie it all the way to the new bumper and air dam.
As to the front of the trailer I had a vision of an upside down and backwards NACA inlet shape, starting mid cab roof and tapering back and up and out, going halfway up the face of the trailer and getting very close to it. I'd articulate the outward parts to allow for the trailer turning, but keep the gap around 6" or so.
I'm hoping ( dreaming?) that higher pressure air under the wing that enters around the cab will "blow" that slot and cause some laminar flow across the front of the trailer.