I have a 12 ft by 8 ft Douglas fir pergola that needs some protection from the elements. Ideally, I would like to preserve or enhance the wood color with a clear treatment, but I'm not totally opposed to staining either. My first main concern is fading from UV, and my second concern is wood rot in winter (when it rains a lot). Any suggestion of a UV resistant and waterproof wood treatment / specific brand and product? I would like something that doesn't need to be reapplied every year, every 2-4 years would be great.