Debee, the thinned epoxy you refer to is known as the Massey Finish, after a noted Alaskan bowyer who used it to great success in the wet north.
1 part two-ton epoxy to 4 or 5 parts thinner (mineral spirits, etc). Apply in coats, sanding gently between coats.
For more on this subject, from people who are experts at the application of the Massey finish, drop on it to the Leatherwall at stickbow.com. There you will find all manner of wood specialists who know what it takes to keep water out of wood.
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