Note that auto paint will not stick to silicone (ask me how I know).
yep and silicone won t adhere to paint well either
silicone is fine for filling gaps but it does not form a very strong bond
Don’t use duct tape when there is metal tape.
The reason that either polyurethane or silicone will work is that this is not a structural application. And the surface needs to be roughed up to make sure either will adhere well to the bond zone. But polyurethane is probably less expensive, and some clearcoats are polyurethanes.