I've done a lot of riding and touring in wet weather on Brooks and can wholeheartedly recommend generous waterproofing of your preference among 1)proofhide; 2) Obenauf's; or 3)SnoSeal

and as to the best saddle cover, the superlative choice, bar none, is an Aardvark neoprene saddle covers in SMALL.

Distributed only from Cyclone Cycling products out of Portland, tough to track down but the BEST saddle cover on the market for Brooks. Greggs' greenlake cycles in Seattle can sort you out one if you give them a call. Ben's Cycles in Milwaukee might have them too.

the small fits like a glove, the regular Aardvark cover fits Brooks loose and sloppy. its worth finding a small. ask your LBS to try and order one for you but i've only seen the regulars in most of the wholesale catalogs.

Aardvark waterproof saddle cover, SMALL.