Hi
I usually use only Danish or Tung oil on my primitive bows. Tru oil seems to have too much shine and looks kind of not primitive, if you know what I mean. Beeswax furniture polish will give a damp proof coat for a while and add more as you go. For waterproof I suppose polyurethane will do it-but really it looks to, er, manufactured-I never use it. Heavy rain will get through any oil, but when you get home dry the bow off and put more oil on, the bow then starts to build some real character!
I re tillered an old bow that has had at least twenty coats of Tung oil put on. The penetration look like no more than about 5 thou', so I think it is only a surface protection.
Now if anyone could tell me me how to keep my fletchings dry when it's bucketing down I'd be grateful