I had a very wet trip a few years ago with my Sherpa. When I got home I could see a bit of water inside after I took the seatpost out and used a flashlight to look inside. The previous owner of that frame told me that he had applied framesaver to the frame, so I did not worry about rust. I left the seatpost out of it so it could air dry. I have several bikes that I regularly use so it was not a problem to leave the seatpost out for several weeks. Not much air flow into the tubes, but eventually dried out.
If there is a screw in the bottom of the bottom bracket shell to hold a plastic cable guide in place, you could pull that screw out to see if any water drains. Or, pull the seatpost out and tip the bike upside down.
One common way to reduce water inflow into the seattube is to grease your seatpost. The grease is supposed to act like a water proof seal. It also is intended to reduce the chance for dissimilar metal corrosion that can lock your seatpost into place, but most of my seatposts are painted so I do not worry much about that.
A couple years ago I bought a used mid 1990s Bridgestone mountain bike from a neighbor for $5 USD. It had been stored outside for over a decade. I had a lot of trouble getting the bottom bracket out of the frame, it was rusted in pretty well. But otherwise no significant rust damage to the frame. I applied frame saver to the frame and reassembled it with a new bottom bracket and a lot of other new parts. It now is my errand bike and I store it outside. See photo.
I think of the derailleur Nomads as Mark zero, but that is not really correct either. There was a Mk I Rohloff Version which came after yours.
