I drove from Washington to California Monday and Tuesday and while I saw a lot of RV's including some small stickies, I did not see any Fiberglass trailers except one in a storage yard somewhere in N. Cal. I think this is the first long trip I've ever taken without a sighting. I saw more right up on Whidbey Island than I did on this whole trip.
Speculation: most Fiberglass RV'ers only take weekend trips? I was traveling on weekdays.
Or, most take other routes besides I5? (I usually do but didn't this time.)