I would not immediately start to seal now until you determine from where the leak is occurring.
Dry the inside completely as best possible.
Find the source of the leak. If, for example, it is a window then it might be prudent to perhaps remove it to inspect the full extent of the leak and how much water got in. All of this will help determine next possible steps.
I agree with Sidecar... it is sorta' like closing the gate after the horse got out by trying to perform long neglected maintenance.
Sold the TC, previous owner of 2 NorthStar pop-ups & 2 Northstar Arrows...still have the truck:
2005 Dodge 3500 SRW, Qcab long bed, NV-6500, diesel, 4WD, Helwig, 9000XL,
Nitto 285/70/17 Terra Grapplers, Honda eu3000Is, custom overload spring perch spacers.