I've never heard of a Parker with a blistering problem, and have never seen it reported here either.
Doing the prep work before paint is the most important part of the process. I use Interlux Micron CSC on my boat which is an ablative coating. Interlux has some good information on prep and application on their web site.
http://www.yachtpaint.com/usa/
Striking the line properly for the waterline (and the overlap) is something of an art. This is where the experience of your Parker dealer, or your local boatyard comes in. Set the line too high and the paint job doesn't look right with too much antifowling exposed. Set it too low and you end up with growth and barnicles on the gelcoat where the hull is not protected.
The surface must also be prepared properly before painting to remove the mold release wax. The surface must also be roughed up sufficiently to give the paint some 'tooth' to stick to the surface. Shortcutting the prep process is a recipe for a disasterous paint job experience.
Applying an epoxy barrier coat isn't required, but many people like to do it. Another option is to paint the first coat of bottom paint in a contrasting color to the topcoat.
Do the first coat in red (for example), and the topcoat in black. That way when the topcoat has worn away so that you can see the contrasting color underneath, you know its time to recoat the bottom. This keeps build-up to a minimum.
Hope this helps!
