I know your pain on removing the old glue from the roof. I used a dynamat type product on the roof skin, followed by a 3M adhesive sound blanket type thing. The silver stuff made a significant differance in reducing the tin can effect.
I would be a little paranoid putting something directly over POR15 without following their recommendations for topcoat. That stuff is incredibly hard and slick after it cures. I could easily see all the seam sealer peeling the first time you got about 30 mph.
SEM 29392, Black Seam Sealer is a flexible, non sag seam sealer for interior and exterior seams, joints, and voids that will not shrink, crack, chip or discolor. Fits standard size caulking gun. No special applicator gun required.
I’m not an expert by any stretch. Lots of guys like to use the expensive two part sealer, but I kinda consider that overkill for a project like this.
so I am continuing this build for pp21, would not bet my life i will make it as motor still waiting for rods, but continuing as if it will show in time. today started some Noico on inside of roof, had to stop, its hot here today, Im sweating like a ___!