We'd recommend our Superior Danish Oil as this will penetrate the oak and maintain a natural appearance. You may find that a few light coats of the oil will waterproof it sufficiently. We would recommend to treat all faces and edges with the oil before fixing to prevent moisture from 'sneaking up' on the finish from behind. The oil will also act as a primer for any solvent based topcoat. Please produce a tester piece and see how it looks.