Riding your new saddle in the rain will destroy it.
Hey, I have an idea...follow the instructions that Brooks provided and not someone on the internet. Sure it will take longer to break in the saddle by following the directions but you won't risk damaging the leather and ruining the saddle. I have a feeling that since Brooks has been making leather saddles for over 100 years I bet they know how best to care for them.
The only thing I do outside the instructions is I apply Kiwi Neutral wax to my saddle about once every 3 months, but this was only after I followed the break-in procedure that Brooks outlined to do.