I've just noticed that in the manual it states that the Rohloff shouldn't be on a bike rack & driven for long periods in the rain ? ...
Perhaps that part of the manual was written from the bike enthusiast perspective and not from a technical standpoint?
1) The Rohloff should not be on a bike rack: Of course it shouldn't. You paid all that money for the luxury of a great bike with a superb IGH, so get it off the rack and go for a ride.
2) The Rohloff shouln't be... driven for long periods in the rain: Obvious really. The Germans DRIVE bicycles. That is the verb they used and translated literally. You'll never enjoy 'driving' your bike when you are getting a soaking. So wait till the weather improves and go for a ride then.
Basically, this is just an appeal to ride your bike more often