I don't know much, but will pass on what I DO know
I've considered this in the past. Even though we have yet to own an RV, other than a popup we used one time and just sold yesterday... Seemed to me to be a good way to pay off a motorhome.
I once talked to a local guy that rented out his motorhome. Not through an agency, but directly. He said that insurance is available, but I didn't find out details. Sorry.
His approach was to buy lightly used motorhomes, rent them out for a few years, then replace with another lightly used unit.
I didn't rent his because he only rented it for in-state use, and we were looking to rent one for a trip to Colorado.
He also mentioned that he had one with a slide-out, and had a lot of problems. IIRC he said that renters weren't taking enough care when deploying it, and it kept getting damaged. So after that he only bought MHs that did not have a slide-out.
What turned me off to the idea was when my wife, with her incredible insight, asked me how well I would handle it if someone damaged my MH.
Nope, I ain't got the personality for it...