5 years ago I built a wooden camper shell for my F150 using parts from an old shell and a few newish parts from RV's. I found a 3' by 1' horizontal opaque hatch at an RV recycler for $30 and used that to access & ventilate most of the extent of the shell from the right side. There was space on that side for a window, but I didn't need it to open, I just wanted a view port and a source of light.
I cut a rectangular hole 9" square in my 3/8" plywood side wall, painted/sealed the wooden edges, put an 11" square piece of clear acrylic from the inside, seating it on a bed of silicon caulk, which also sealed the edges of the plywood to the surface of the acrylic. From the outside the window is recessed the thickness of the plywood with a bead of caulk all around, there is no window frame visible from the outside. From the inside the edges of the acrylic were secured to the wall, covered & trimmed with a very thin wooden molding rabbeted the thickness of the acrylic.
This window has been exposed to all weathers for 5 years and has not leaked, loosened nor needed any maintenance besides washing. The only flaw is a subconscious wish to see a external frame/molding around the window, though none is necessary.
