There was nothing to fill the gap from the factory and water likes to pool up in the bottom, especially the corners. The urethane is recommended to stop this.
Special caulk gun? I used a hardware store gun when I applied the seam-sealer. Your guy might be BS-ing you.
The caulk tube "looked" like it could be smaller than a standard tube, I dont know...it had a "pop top" end cap....sound right?
Do you just caulk the trim then? Or do you need to pull the trim and urethane under it?
Seems like caulking the trim would work to stop water from getting in there to begin with, though I have to wonder how its getting into the trunk.
ANyone have pics of a urethane'd window trim?