The RT is now weatherproof! It's been through moderate to heavy rain and has nary a leak, thank goodness.
Amazingly, the entire interior dried out and the neutral and somewhat pleasant scent that was present before the water exposure is just as it was and there are no water marks on any fabric materials. I'll call that a miracle.
We have saved many many dollars over the years performing DIY projects, and the time and hassle saved by not outsourcing projects is certainly valuable. But sometimes it's not worth the potential bad outcome.