The corner rock guards on our '83 Excella had several cracks where they had been hit when we got the trailer six years ago. I removed them and placed them outside down on blocks. I used used a diabetic syringe to apply acetone to the inside of the cracks, being very careful not to apply too much so as not to remove the clear shine. Those small cracks have never spread.
The rectangular center section had become, over time, concave. I removed that panel from the coach, removed one of the long sections of the frame. I then slid the plastic panel out, turned it over, and reinstalled it placing the convex side out. I'm so I reassembled and reinstalled the guard. That was a year and many miles ago, and that panel still looks great. Slightly convex looks good. Concave just looked old and misshapen.
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