i have used many times exterior household sealer.

Once metal work is done and primered prior to paint.

Apply it first with silicone gun gun and follow up with a paint brush.

I soak the paint brush whiskers in thinner prior to spreading the seam sealer.( it spreads easier)

Once painted it looks very close to OEM,

Ive done this method several times for the last 10 years and never as one cracked.

Not to mention some of these cars are stored in unheated garages .