I have a 32ft Class A diesel RV (my wife named it "Big Brown Bessie"). I only use it a handful of times each year and I often I debate renting it out. But given you have to have a Class B license to legally drive it and it is a very complicated machine I just don't think I could turn it over to someone who's "green". I have debated trying to rent it out, I drive it to location (within reason), set it all up, hook up all the stuff then leave the renters. Then when they are done, I come break it down, I drive it back home, clean it and they are on their marry way. But my guess is that people that rent an RV, like people that rent a boat, want to drive it. That's half the fun right? (That is until you got a crosswind and passing semi's then your mind might change a little.)
And honestly I think after a few weeks of that I would pull ad as would likely be more hassle than it's worth. The only people I really see my possible scenario benefiting are people that are on the fence about buying an RV and just want to take an "extended test drive" before they blow some major coin.
I never thought about renting boat but as anal as I am about it I don't think I could do it. Would maybe consider it like scenario above, but again I'm not sure the hassle is worth the $ (for me). If I was retired or single or needed the $, then maybe. Although the waters around here are shallow and if you don't know what you are doing you can get in trouble fast.