Has anyone got any tips on repainting a foam sandwich PT? The boat has got a coats on it and I would like to get back to original to save on weight.

As fibreglass is waterproof, there's no need to paint it.
Foam-core boats come with gel-coat, which forms a hard outer shell that protects against scratches and damage. This should last the life of the boat. For example, I've had a 40year old fibreglass boat and a 30 year old foam-core boat that had perfectly good original gelcoat.
If the gel-goat has gone all dull and powdery, just polish it with car wax. You might then remove the wax with dishwashing liquid, as the water-repelling wax can be slow in a drifter.
If the boat is damaged with scratches and gouges, fill these with bog. A cheap car-bog / body filler is fine. Eg: www.supercheapauto.com.au/online-store/p...d=220284#Description
As the boat is polyester, I'd stick with polyester based products, rather than epoxy. Alternatively, see what an epoxy manufacturer says: www.westsystem.com/ss/polyester-over-epoxy/
After making it all nice and flat, you could sand the boat with wet & dry sandpaper, then spray fresh gel coat.
For more info see:
"Re-gelcoating" at: bertram31.com/proj/tips/re-gelcoating.htm
"Gelcoat repairs" at: www.fibreglass.com/techgel.htm