A lot of people overlook the support aspect and end up with warpage along the way. If it were me, I'd takeout all of the old material and rebuild back better and stronger.
I saw some discussion about epoxy and traditional resins. Epoxy sticks to everything if it is prepped well. Poly and vinyl esters will stick to epoxy but it is a mechanical bond and has to have good clean rough surface.
I just got a 6-foot level yesterday. Before i fiberglass anything, the hull will be flat.
From what i read, epoxy is the best to use and most expensive.
I don't need the best, and i don't really like working with epoxy.
The boat was built with polyester. Least expensive and has not failed yet and probably never would.
I plan on using vinylester laminating resin. For me, it's the easiest to use and what im familiar with.
Better than poly, but not as strong as epoxy. Middle ground on price.
The hull is 38 years old and the fiberglass has not failed even with all the less than ideal construction i have found.
Honestly, with good prep work anything i do will be as good or better than the factory did.