I was just going to suggest silica as well -- but in a different way.
Someone suggested a storage box - Target sells some that are in theory water tight. Couple that with a silica pack designed for gun safeslike these, and toss them in the oven every couple months or so when they need re-charged. Nothing to add to your rub bottles, etc., and should help with the clumping.
I think I'm actually going to order some myself now....
First, ignore anyone that uses the word "rice" in this thread!
If you want to DIY it, put it in a plastic sweater box with a bunch of desiccant packs, you can buy them online.
If you're really concerned, send the camera, back and lens to a legit repair service for a look-over. MamiyaRepair.com is probably your best bet in the US. If you tell your insurer that you're getting and estimate, they'll usually leave the case open.
If you body or lens has never been serviced, with an RB it can be a life-extending investment anyway. A guy like Bill (link above) has all the factory rigs to check tolerances, and he knows which lubes go where and how much to use. Winding mechanisms and mechanical parts may last a lot longer with tolerances adjusted and fresh lubricants, and lens shutters that start to seize usually just need a proper service. this stuff can add years/decades to an RB's useful life, but starting off with an inspection may not be a bad idea, and I imagine you could get a repair guy to agree that any servicing is needed because of the flooding.