Duct tape sticks well, and the black and silver on my Insight has lasted well. Chrome on the Escape also lasted well- but keep in mind residue after the fact- I left painters tape on the Mustang for 24 hours with a little sunlight and I
still have some residue left
As far as you are, I would try to do a full boat tail. But for me, I took my bike rack and built a wooden frame, then built the coroplast onto it. Wood, nailed together, then fiberglassed over, and super zip tied. This was attached to the bike rack. This might be confusing so I will try again to be clear...
I attached the bike rack. Measured what size I wanted to fit, and kept those measurements. I built that piece, then examined Metro's build, and used his ratios to get my length. The final end was just big enough for my tag plate, and the cp flows from the wood frame at the end, and then to the plate.
My plan for my kammback was to use PVC piping to build the frame, and use some insulation for safety on the window/paint (this would be secured with the bike rack). It is fairly cheap, but it isn't free :/ L joints are the same way, I am not talented enough to build without them lol.
It's nothing solid, but this is how my mind put together cheap and cheerful, so it might be helpful to you or inspire you to think of something better
