The spar urethane will work, but spar finishes are made to be able to expand and contract as outdoor wood swells and shrinks and therefore are a softer finish, and will target burn pretty bad. Most regular oil base polys will burn very little or not as all if put on in thin coats. Helmsman will yellow more, too. I've had good luck with the Minwax or Zar brands, same as Magnus above. Get the gloss, it is harder than the satin. Glue with Duco, or Saunders NPV.
Bohning is a pretty unique formula and doesn't generally play well with others. It is a lacquer, so the poly shouldn't lift it, but I don't know that it will stick to it, either.