TWP(Total Wood Preservative) is an excellent product. I've used it for 4 years, and never had any problems with a deck turning black, and I live in a very humid climate. With proper prep and applied properly, you can expect 2-3 years color retention on a flat surface.
TWP does not contain natural oils, such as your Wol..., Pen...., Be.., ect...
Natural oils attract mildew which will turn a deck black in no time, especially a cedar deck.
I would put TWP's RADCON Formula (Natural Cedartone) against any natural wood preservative out there, and I'm surprised more contractors don't use it. We also use it on log and wood homes.
Ask Tim Cross, He's used it for 10+ years.
Jim, I'm not real familar with the North West climate. We have a problem with lack of rain here in the South East. Possibly you could add more mildecide to it.
Just my two cents,
Larry Staton
Georgia Wood Care
Larry@georgiawoodcare.com
p.s. TWP and Ready Seal are very similar products.