RE: Hawker Tempest Project!
The first thing I would try would be to thin your epoxy with 30-40% denatured alcohol after you've mixed the hardener into the resin.
If I still wasn't happy I would seal the balsa with some thinned out clear dope (maybe with a little baby powder) then I would repeat with the above.
What are you planning on doing with this wing and what kind of internals are you thinking about?