RVs depreciate like boats, yes. From friends who have had both, and several who divide their year between their boats and an RV, it's my impression that the boat requires more upkeep and extra expenses than the RV. Maybe it's just the corrosive effects of salt water, etc.
We live fulltime in our RV, which affects upkeep. Obviously, if it was stored part of the year, costs might be different.
We generally budget a regular amount every year, in the neighborhood of a thousand or two, for maintenance and upkeep on our RV. We've had it nine years and some years, most of that budget has gone unused, but we do a lot of the basic maintenance ourselves.
We've been lucky. We have a quality motorhome and have had no troubles with it. In the nine years we've owned it, it broke down once, and the trouble turned out to be a sheared bolt in the engine. No other troubles or expenses for repairs, really. All expenses have been things like regular oil changes, fluid replacement, brake checks, etc.
Since we are fulltimers, we tend to look at these maintenance and upkeep issues as compared to home ownership, and in that sense, the RV comes out looking really, really good.
If one were looking at RV expense in addition to a home and all its' attendant costs, then I would suspect an RV would be much like a boat, something that it feels to you is always soaking up money.
LooseChickens