I do not like pro-seal….
3M 5200 is an excellent adhesive/sealant for bonding things like fiberglass, plastic and metal. It’s designed with marine conditions in mind, but works well on aviation hulls too. It has a very high tensile strength and is available at most hardware stores in black, white and mahogany colors… MUCH easier to work with than P-S and more applicable when not dealing with a fuel tank. It is not silicone and is paintable.
The only downside is that the standard cure takes about 3 days to achieve full strength, but provides a ”tough, yet flexible, polyurethane polymer” retention and seal for things like ducts and vents.