Gen 4 2016 Prius water leaking into Spare Tire well

I recently purchase a used 2016 Gen 4 Prius and noticed a musty smell during the purchase. Got the car for a decent price, figured I could easily get rid of the smell. Well, turns out the the carpeting in the rear seating area was very wet. Floor carpet was also damp on passenger side front seat as well. After some extensive searching I found that there was so much water in the spare tire well that when I would brake it would wave forward into the back seat floor area, then once that was soaked moved forward once again. The car has rubber molded floor mats so your feet were not wet. BUT, I bought the car in the winter and had the very odd problem of windows frosting from the inside when you parked out at night. (due to high humidity) The previous owner never parked outside. This clearly has been going on for a very long time. (all of the above is meant to make this thread easy to find)

Anyway, piece by piece I have disassembled the trunk area, I now have the spare tire well open, which during the last rain storm identified slight water dribbling in from under the side-panel at the very back. I've since removed the side panel and am now waiting on the next rain.

Note: behind the side panel I found a pink drain hose, which I assume is part of the sunroof drain? I checked that hose for cracks and clear passage, it all seems good.

If anyone has any ideas of where I might focus my attention, I'd love the advice. In any event I will keep this thread updated until I find the problem. Right now, the solution is to leave one of the many spare tire well rubber plugs out - LOL Found many posts on this issue with the Gen3 and now it seems Toyota has made it easier in later models to drain your spare tire well.

 

Getting closer. It rained on Monday and on Tuesday I found a small puddle on the deck right below where the hatch seals. To give you a visual of where; If the rear panel interior finish were in place (which is currently is not), the puddle location would be between the rear panel insulation and the inside of the rear quarter panel.