I would go ahead and use real varnish. Epifanes from holland. Put it on as per the directions, if its too glossy, then knock the gloss down with some fine bronze wool. You can always paint over it later, if you want to change the look, or get tired of the maintenance. After five or six coats of varnish, any tiny holes will be filled, and water proof. The advantage of the Epifanes, is that it is very flexible. Tung oil won't really build on the surface, and give you the protection you might want, that is, if you drive your truck in the rain, and leave it outside. But, oiling is much easier.
My 2 cents.
