When you sealed your roof, did you use eternabond tape? Something you wish to consider since its use will last longer than Dicor sealant and give you more peace of mind.
Please share pics of before /after and how your vinyl wall covering looks. Would love to see your experiences in this repair.
If you have fiberglass delamination, that is easily fixed by injecting a compatible epoxy into the delaminated areas and pressing the "sandwich" back together for 24 hours. The repair is usually stronger than the original composite wall.
Also, I've seen walls replaced with lightly stained pine planking and looked really nice. I've got a rear wall I need to fix and I think I'm going to use pine wood wall panels.
Here is a link for RV wall paneling made of composite Vinyl with Luan backing in 4x8 sheets.