Read this thread about living aboard: Living Aboard Cheap- Dreamers read!
The truth of the matter is...its a hardscrabble life to do it on the cheap. You prepay for housing and then have to scramble to just get by (unless you have funds, in which case, its almost always easier to live on land).
Some prefer it, but like in most things...try before you buy!!! (ie, see if you can live aboard somoenes boat for a few weeks before buying your own).