Here's what I'm looking at building. You are right regarding cost. I have no idea what this will work out in terms of man hours and material.
Dowels/tent poles are attached on the vertical corners from the tailgate to the glass window, holding up the weight of the "cap."
The "inner gasket" is the inner most layer (closest to the bed) and is attached with velcro tabs attached to the carpet kit of the snug top.
The mosquito net is the middle layer. It has an upside down 'T' shaped zipper (actually three zippers) to get in and out.
The outer shell is waterproof and is the outer most layer. It has the tent pole gussets in the four corners (outermost corners of the tailgate and snug top glass). It also has a 'V' channel attached to the horizontal edge that runs along the glass window (hinge edge) and the tailgate (also hinge edge) with maybe some elastic or sinch down mechanism to tighten it up.
It looks like this:
I will make a model tonight or the next to make sure this thing works. Like I said, meeting with the guy on Friday for cost feasibility. I'll let you know what I find out.