Oak. Spar varnish. Reapply every year as needed. If it works for a sailboat, it should work for you! You could also use several coats of epoxy with a uv inhibitor to reduce discoloration.
Sascha Steinway TLCA # 20217
1977 FJ40 "Ripper" (because it shreds!) (What is a "shread"...Steve Crase)
1988 FJ62 "Dino" OME, now in the hands of my daughter
2013 F-150 "Black Ops"