EDIT!!! Jeezum, I just noticed this is a seven year old ZOMBIE thread!
Nevermind....

Wise choice. The above mentioned "guru" reminds me of some of those whacky cult leaders. Dead wrong. Oil only will prematurely kill a fine saddle, unless used very sparingly. But that's why they make Proofide. So you can control how much oil goes into the leather. Very little, ideally.
Some great advice here. And some not so great.
Listen to the manufacturer. And if not them, the guy who contracted Brooks' saddle repairs for roughly two decades,
Tony Colegrave. He is against putting Proofide on the underside of the saddle, as it clogs the pores and doesn't allow the leather to breathe. Which it needs to do, especially when it gets damp or wet. The suggestion of using fenders on a tour like yours is a must do.

Then again, if you are taking your kids on this monumental tour, you'll have far more serious concerns than your saddle!
Good on ya! Sounds like an amazing, once in a lifetime adventure.