OP Update
While starting with asking the RV dealer for suggestions may seem obvious, I had avoided doing that expecting that I would need to drop off the trailer for them to repair and pay a fortune in parts in labor. Turns out they have coroplast available from a 70" roll that you can buy by the foot to fix it myself. Perfect! Except they are low on stock and I'll have to wait a week or so for them to get more. The sheet that came off is 70" wide that spans the distance between the trailer frame rails. Must be an industry standard. I believe they said $7/ft which would make it only slightly more expensive for the replacement parts than the ~$22 per 4'x8' sheet from Home Depot. Plus I'd much rather have it be a single continuous sheet going back on than multiple sheets. I'd be afraid of air getting between the sheets and ripping the whole setup off again.
