We did the repair today without difficulty. We decided not to caulk the plastic trim in place and just tighten to allow us to slide the trim around in the groves and so get extra tightening. We cut off an extra 4 inches off the lower over-the-cab trim after reattaching one end with the original screw/washer, slipping the top trim edge under the upper groove a few inches at a time all the way around, popping in the lower edge into the lower grove along the way, and then sliding little bulges of trim around the whole over-the-cab to the unscrewed end (do not pull, push around like getting bulges out of a 10'x30' carpet). Make a pencil mark where the screw hole is before covering the screw hole with the trim and install the tail end screw/washer. Cut off the extra trim.
Looking at the even longer upper trim raised the issue of when will that trim pop out. We removed the single screw at the rear of the camper on the upper plastic trim, reinstalled the screw to hold one end of the trim in place while holding the now loose end, and pushed little bulges of trim all the way around the camper to the loose end. We reinstalled the screw to now hold both ends and cut off 10 inches of extra trim off the upper trim.
You can check for loose trim by pushing along the trim on a long run to see how much it moves instead of having a failure occur on the road.