I have read here about using FRP in place of the interior shell. My '77 Sovereign's PO, who I shall refer to as Skippy, pulled the forward sections, from the entire nose rearward to the first straight sections and sold them for scrap aluminum. He also performed several other questionable "repairs" to the old girl, which I will handle in due time before we can hit the highway.
FRP, readily available, and easy to work with, would be an easy fix. However, using it in a trailer which flexes and vibrates, I believe, is a bit beyond what its engineers had in mind. I know more than a few fellow Airstream Remodelers used FRP. Any problem with stress cracks?