As for how i attached the foam. I used the pre glued stuff so that tool care of one side, the other I used caulk and epoxy to attach it to the car.
In your case I would try hot melt glue (glue gun) it will stick to the plastic and the foam yet be removable if needed.
from the pics it looks like you got some wrinkles in the coroplast, how much tension is on those?
How is the rear view out the back?
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