Of course I cannot disagree with thrillhouse more. Polyurethane paints can be difficult to get right the first time.....but none of what he mentions is impossible. There is a learning curve with these paints.
If you are dead set on a spray paint, then I would suggest using one of the marine paints that can also be applied using a sprayer. Doing it that way certainly has its own challenges, but if you have the correct equipment, the right safety gear,.......and the skill, marine paints are better suited to boats.
The thing to consider is that any specialty paint system takes a degree of developed skills to apply. Just because it says you can use a roller and a brush does not mean it is as easy as painting the walls in the den.
just my opinion...........and my experience.
BTW- If you decide to use an automotive paint system you will be glad it is "easy" to touch up. After awhile on the water, you will have plenty of touching to do.