Hey Dan,
My truck is a DD or at least a couple of times per week driver and I wanted to be able to repair the finish without much trouble. So it is just a black deck stain rubbed off and finished with Olympic waterproofing. Hasn't seen much weather yet so I don't know how it will work out.
Mar-K has a great technical article on different bed finishes and has pictures after various numbers of years in the weather for each one.
http://www.mar-k.com/wood_finishing.html
http://www.mar-k.com/wood_finish_testing_i.html
http://www.mar-k.com/wood_finish_testing_ii.html
Oh yea, mine is red oak.
TR