I salvaged an old Brooks saddle, (Professional) that had been hanging in a barn for a LOOOONG time. After a couple of liberal coatings of proofhide, it is in good shape. I use it currently on my MTB, and may move it over to my Roubaix if I decide the Spec BG saddle isn't comfy enough. The only real issue I have with the Brooks is the rails are short compared to modern saddles. Oh, and due to leather drying and pulling away from the rear rivets, I had to take a mallet and tap down the copper rivets to smooth out the edges of them in line with the leather after all the years of drying.

As for a saddle cover, I'd carry a plastic grocery bag with me if I was going to ride in the rain.