I have a long bed and an extended cab, so mind was going in that direction opposite the camper bed layout, lol.
I have thought about a roof rack faring. My TC stops at the windshield, EW ;)
Since TC is fiberglass I will not be drilling anything into it. If it were plywood and aluminum siding then I wouldn't hesitate to drill and bolt into it as kind of hard to ruin cheap.
Still, my thought is that if your hood deflector is kicking the bug line up to the camper, then it is pushing the air above the gap. I am as interested in increasing mpg as I am keeping bugs out. I can get 16mpg with TC and a cargo trailer, so am doing pretty well there, but any extra is nice.