Primer is not just for building up and covering imperfections. The real purpose of primer is to adhere to the surface you want to paint and the paint then adheres to the primer. If you take a shortcut and skip the primer, your paint may peel off in blotches in places where it didn't adhere well. More than just 'sticking' to each other, it is more of a bond, something we want to happen.

Shortcuts, with anything we do, usually do not pan out very well.

I think anyone would advise you to spend the required money and spend the extra time to do it the right way. You will be glad you did afterwards.

How about just varnishing the whole thing?  No primer, no fancy thinners and it looks great.  Many on this site have had good luck with mid priced varnishes. I have put 3-4 coats on 2 boats with one quart.  The coats were put on with cheap foam brushes so they are thin, but it is easy to sand and apply more at the end of the season.

The key to a good varnish job is your labor, not the cost of the materials.  The point is to protect the epoxy from UV damage so perfection is not needed.

Thanks for your responses guys.  I have to use paint on the bottom because of imperfections caused by the previous owner.  Looks like I will have to buy the primer and give it a go. The top will be varnished using scooner varnish from CLC.  What about thinner for Brightside?  Is it routine to thin the paint up to 10% with a special thinner (216), or can the paint be used un-diluted? 

It's best to follow the thinning instructions to get a streak-free finish.