As noted in another thread, oil finishes
Posted by: g2d on Nov-03-12 1:27 PM (EST)
in general contain a varnish component. The thinnest oil I've used, Minwax 209 clear, contains a varnish component.
But that varnish component is not as effective a sealer and surface hardener as quality spar or polyurethane varnish.
Others have pointed out that even thin oils like Minwax 209 leave only a very thin layer of penetration.
And I'll just say again that increasing moisture content will weaken wood somewhat. Epoxy and varnish minimize moisture infiltration. Oiling? I don't think so.