Use what many private
Use what many private aircraft owners use on their aluminum aircraft, and the US Navy uses (salt spray environment). Corrosion X. I’ve bought it in spray cans. Penetrates through dirt, displaces moisture, flows slowly in hot weather. I shoot it into my F150 body and box through every hole i can find. Pull the weather strip off in a couple places around door frames where attached by holes. I do it every other summer, but it should last at least 4 years.