[Bicycle Bob]

Perhaps what you need is some foam plumbing insulation. It can be carved with a knife and glued or taped on just behind the door to give a new surface with a rounded edge. At the back, just use it as a shim and continue the Coroplast back at a gentle taper.
To remove panels for service, a tape job can be planned so that a single stip of tape does the mounting, and it is easy enough to peel for re-use on the road, or easy replacement. You can buy a lot of tape for the price of a latch plus installation. Using coloured duct tape does wonders for a professional appearance, and plain vinyl top coating tapes are more durable in the weather.
For a neat appearance and a reinforced bottom edge on Coroplast skirts, just slit the inside surface of 3 adjacent flutes, fold over, and use double-sided tape.