If the OP will look into Yahoo Auto Groups, he'll find one called 'Classic_B_Vans'. It's pretty much misnamed, since the majority of postings there deal with smaller C's, mostly from the 70's thru the 90's. There is one poster who regularly posts a group of listings from Craigslist & eBay, simply as a public service. Scroll down the postings to one called 'This week's selection...' posted by baldwiny.
A fair percentage of these meet the criteria of fiberglass roof and / or sides. I've seen several recently that I would seriously consider buying if I was looking for a budget RV. As a bonus, he & other members will often post their comments / opinions / experiences with these & similar units.
Here's a quickly-selected example from his latest post:
https://maine.craigslist.org/rvs/4505927837.htmlThere's also a photo file there that shows member's present and former units. It's a fascinating time killer for me.
Jim, "Mo' coffee!"