Hello John,

You may find that resin only will probably not be the best long term solution as the balsa weave will most likely show through over time. In addition to applying a light layer of .6 to .75 glass cloth with quality laminating resin to the affected areas as suggested by others, I would also generously apply a lightweight "hi-fill" to the entire surface (brushed/dabbed on) after glassing. Let the hi-fill cure completely, and then sand back using a rigid sanding block. This method will avoid the issues of sanding through the glass into the wood, etc. You will then be left with a perfectly flat surface ready for priming.

Best Regards, Frank