And I enjoyed eating the steak it provided too.

If you can get across to Canada and an MEC store, see if you can pick up one of the saddle "condoms" they stock. When we went to an MEC in Vancouver early this month, I found this really neat latex rubber saddle cover that is appropriately shaped and simply stretches over the seat. The opening sort of gathers around the seatpost. With fenders (or a rear rack or in our case a seatpost rack to support the Carradices) I expect it to be a great solution to keeping the Brooks dry.

Proofide underneath is a good move anyway.

Light rain is not really an issue as pdlamb points out (safe in the knowledge that Brooks hasn't found a lamb or sheep hide thick enough to make its saddles from... yet!).