When I started building my gap cover fer my cab to camper gap, I looked at everything.
Adhesives won't have enough holding power because as soon as the air catches underneath it, it will git ripped out in short order.
You could try some expanding foam to git the shape you want but keep in mind that the truck will flex and the nose of the gap filler will git impacted by the back of the cab. You want to distribute any force across the face of the camper that the air is gonna to apply to yer gap filler. Once you settle on the shape, I would use some latex paint to protect the foam with.
The solution I eventually settled on was a cover that floats on top of the cab and my aero cap (aka front access doors) that are hinged. I have some Tyvek tape on the cab to allow the rubber gaskets to float on the cab due to flexing of the truck frame. I need to upgrade it to some 3M clear 5 mil plastic film as the Tyvek tape is worn in spots.
This was one of my first attempts on a gap cover.
http://ecomodder.com/forum/showthrea...gap-14058.html
BTW...where abouts in Texas are you?