My boat was painted with oil based porch and floor enamel, gray on the inside and dark green on the outside.  The boat was primed with an oil base primer.  Much of the interior is still the original gray, although I did redo the floor with Durabak just now.  I would have freshened the exterior with the same paint, but Sears no longer offers porch and floor enamel in oil base.  So, I repainted the exterior with Petit Easypoxy.  The Petit paint is pretty, but I don't think it's quite as tough as the Sears paint was.  Other paint suppliers still do have oil base porch and floor enamel and I'm sure they'd work.  If that doesn't answer your question, please feel free to get back to me.  Good luck!

I'm in total agreement about keeping costs down and doing things in a practical fashion.  Hope the porch and floor enamel works out for you.