Long ago, we had a blowout -- the flapping steel belts tore out the trailer’s thin sheet metal wheel well. (I rebuilt it eventually, but the trailer was pretty well-ventilated until then.) My new trailer came equipped with thin plastic wheel wells, which looked similarly vulnerable. I understand that the trailer was designed to be lightweight, but I wanted more protection from blowouts and road debris.
So I went to a nearby truck stop and bought a big sheet of mud flap material, very thick and heavy. It was less than $4 for a 36 x 30 inch sheet! Using tin snips, I cut it to fit the top arch of my wheel. I then cut a semicircle to fit the vertical inside wall of the wheel well. I used Gorilla glue to fasten the “armor” to the plastic surfaces. Since Gorilla glue has to be clamped, I used spreader clamps to push up on the “armor,” using the tire itself as the base for the clamps.
Here are two shots of the armored wheel wells -- you can click on the picture to enlarge it, and click back to get back:
I was not sure if the glue would hold, but so far, so good -- we took a trip of almost 800 miles to Yosemite and back, through some snow and slush, with no problems.