I am the latest victim of the rusted through drain nipple and the resulting water ingress. I’ve not yet decided on my choice of fixes, however I have implemented a quick fix.
Accessing the issue by partially removing the rear door seal such that I could get my hand between headliner and roof, I have push fitted a length of garden hose over the remainder of the nipple, keeping it in place with a towel pushed behind it, and trailed it into a receptacle on the back seat, per attached pic.

Good idea