I realize these attachments involve Airstreams, but some of the renovations could be applied to fiberglass rv's.
First up is a smaller airstream that was redone for Orvis
orvis airstream - Bing Images
The second one involves a larger Argosy that was renovated in the Adirondack
All involve meticulous metal and woodworking skills and ideas but may lead to someone here replicating some for their own. enjoy...