I don't put anything on my damier bags. It already comes with the dark treated handles and the bag itself is basically water resistance/proof already so I just let it go. My bags like to roam around the city naked/freely.
It's my understanding that Damier is virtually maintenance-free. you don't have to worry about staining the leather -- unlike with the Monogram pieces! I just bought a used Damier tote bag (the Chelsea) from 1999. I brought it into an LV store last weekend and the SA was shocked when I told her how old it is. She said it looks brand new, and it does.