The best way to avoid excess weight gain and still have the strength of the wood / glass/ z-poxy sandwich is to use lightweight glass cloth, pre-cut to size. I sometimes mist a very light coat of contact cement ( spray can type) on the cloth and lay it in place- the tack keeps it from moving around when you spresd the expoxy.
Have old credit cards / squeegees, paper towels and a couplke rolls of toilet paper handy. Place a section of cloth on a part and smooth it out.
Warm the Z-poxy bottles in warm / hot water, mix some up resin and pour some on the cloth. Spread / scrape the resin toward the edge of the part, and scrape the excess back into the cup.
When you have the whole part wetted out and scraped down, take a roll of toilet paper and roll it across the part to soak up more resin- press down & make sure to roll it so it stays on the roll. Peel the loaded paper off after each pass so you continue to soak up the excess resin.
This gets the glass cloth fully bonded to the sub-strate with minimal epoxy to keep weight dowm, and will cure to sanding hardness pretty quick. Hit it with some 220 to knock down the high spots, but don't sand so much the cloth statrs to fuzz up. Wipe down good with alcohol and shoot a good coat of primer to finish filling the weave. Then it is just like any other base- and we know you have that under control from your Helldiver post!