Fiberglass Reinforcemet
Kevlar,
I have no experience with a P51, however we do a-lot of fiberglassing where I work and just completed a 3' wide x 6' long x 3" thick plank made from blue foam and wrapped in fiberglass cloth. We set both ends on buckets and it held me at 240lbs in the center. So to answer your question I would "think" that fiberglassing with cloth, not just resin, would strengthen the areas your are questioning.