We have a guy at my dock living on an old 22' boat for several years now. He works hard as a waiter and the boat goes nowhere and probably has 2ft. of growth on it. He reads a lot of books and has simple tastes and enjoys the life at the docks. He has no maintenance expense except the occasional tube of silicon and simply pays his dock fee and the basics each month and seems quite happy.
So...if that is what appeals to you...it can be done. He is one of the few I've met and most single guys living at the dock tend to be just "temps" or have some sort of socialization problem and tend to move on to the next place once they've worn out their welcome.
Couples living that sort of lifestyle are even rarer as it is most unusual to find two such types married to each other!
My comments here are limited to those who live aboard at a dock...not cruising singles or couples.