[QUOTE=quality parts]I work at Mar-K Quality Parts. We make pickup bed parts. Have been testing wood finishes for a while and you may be interested in the progress. http://www.mar-k.com/wood_finish_testing_ii.html
There are several clear finishes being evaluated that are specifically designed for wood that is exposed to outdoor environments. The current test has been in place for only a few months so there are no failures yet. We post updates when failures or other notable changes occur.
I got my bed wood kit from Mar-K. They recommended a Marine Spare Varnish, so that is what I'm using. I just put the second coat on and it looks real nice. If they could pre finish the kit they would make a mint.