No room for a boat when RV-ing? Then maybe you need a Boatahome. It's an RV, no wait, it's a boat, no wait, it's just too weird. Sales pitch vid here. I so want one - NOT!
I can agree with the sentiment But Generally this arrangement would have less interior space than an RV the same length and weigh more And boats tend to have a wider beam (width) per length than RVs So a 30 ft boat, would might be too wide to tow with out a permit
Why not just get a boat with a cabin? Leave it one the trailer and use it at the campsite like an RV. Then when you are ready to go in the water, pull it in. No different than sitting at a dock, whether wet or dry.
Once I saw a 28 ft sailboat in a pull-thru spot in an RV park. The couple were taking the boat from California to Maryland, and were stopping at RV parks for the night rather than a motel.
Another time, I was a large power boat in an RV park - similar deal. They were taking the boat from the Great Lakes to the Gulf coast for the winter.
The one in the first video was for sale in Calif. a few years back. Problem was it was to long and you had to get a special permit to take it on the highway.