Tried the Benjamin Moore single part urethane. Can't recommend it. I've got 3 coats on, and I still haven't figured out how to get the brush marks to level out. Prior coats sanded with 400 grit, when rinsed off the boat looks like a mirror. New coats are applied with a new sponge roller (half a West 7") then tipped out vertically with a new 3" sponge brush. Little or no leveling of the marks from the sponge brush takes place. I've tried varying amount of thinner and Penetrol and haven't found the combination. The only 'plus' is that I haven't had any overlap problems from one band of paint to the next - even working at my slow pace. Paint, tip, move the ladder, wipe down, paint, tip - occasional pause to re-wet the wipedown rag or get more paint from the tub.
I think my next step is to sand the transom with 400 grit and then hit it with the buffer. If that works, I'll do the rest. If it doesn't, I haven't spent a lot of extra time. I've spent too much already on this job....
Perhaps I should offer my free services to the paint shop at Rockport Marine - might learn some tricks...