i have painted quite a few boats with all types of two part polyurethane and epoxy paints from automotive, marine and airplane finish applications. the three that i found the best were (from best to just great): Sikkens Automotive paint, Awlgrip Marine paint and Imron Automotive paint. The Sikkens was actually a single stage which did not require a clearcoat. this boat has sat in the sun for more than three years and the paint is as slick and shiny as the day i painted it. has not even been waxed yet! had given it two coats of primer and three coats of finish (no sanding in between coats).

some of these paints are quite expensive and the cost may not be justified in your project unless that is the quality you want. the most important thing is the prep... prep and more prep. you will need a top quality primer that is compatible with your top coat. the sikkens primer is almost $ 150.00 per gallon and (as i remember) that did not include the hardener or the thinner. for that showroom quailty paint job you will need a clean room / spray booth. luckily i have a friend that has a paint and body shop that lets me use the facility on saturdays. friday pm i wash everything down inside and out of the booth and spray with a wet floor... also, if you are going to use a spray booth - make sure that you crank up the exhaust fan well before you bring the boat in to remove all particulates form the air... anyway i am getting carried away. one speck of dust can ruin an excellent single stage paint job and make you go with more prep time and a second coat or clearcoat.

the answer to your question is an unqualified yes. if the single stage starts to blush or chalk in a few years you can always lightly wet sand and then apply the clearcoat.

as far as automotive clear directly on wood you will have to get another opinion on how to do it. i have been in the sign trade all of my life and it seems that we tried it on wood signs but weren't pleased with the long term result... any end grain opened up and then the finish blistered in the weather.