West Epoxy can be brushed on as a very good "epoxy varnish". However it will only stay put if the wood is really dry and the piece needs to be sealed on all edges (difficult on a section that is already in place). Any damp inside and the pressure will build up in the sun and blow the finnish off.
Works really well on new wood but I've never managed to keep it in place for any length of time on existing wood.
You've really got the choice of microporus finishes or regular rubbing and re-varnishing.
Classic Boat have been running a long term test on the new high build varnish / stains. Nova Tech etc. Interesting, but nothing looks as good as real varnish, just depends how much time you have and what you need to cover up.