I think the real issue for molded fiberglass trailers is establishing value in the event of a total loss. If the trailer is near-new, it's pretty straightforward. But if it's older (like your Casita), and especially if it's a restored vintage unit, you may find that the insurance company's idea of its value is far, far less than what it would cost to replace it with something comparable.
Consider that it doesn't take much to total an RV. Even a minor collision or a falling tree branch often results in a write-off due to the lightweight construction and high cost of repair.
Print out the NADA or KBB value of your 2001 Casita
, collect a file of recent classified ads for similar units, and have a chat with your agent.
There are agreed-value policies, typically based on an appraisal. Not all insurers offer them, and they are much more expensive. They are typically for folks who have invested significant money and time restoring an older trailer.