J-B weld is excellent for filling in stripped holes and certain other repairs. It is NOT a good surface filler, especially on vertical surfaces. It will slump before it sets, and trying to level it again wrecks the surface. It is very prone to cracking and popping off entirely.
It is also tough, therefore difficult to sand, without sanding through adjacent aluminum in the process.
Bondo or Z-grip would be way better; they are intended for thin veneers on metal that may flex a bit.
Replacing the panel is, of course, better still.
It seems I love the mountains and deserts more than my friends do. I sure miss them!
1971 Streamline Imperial project "Silver Snausage", 1985 Coleman tent trailer, 1964 Little Dipper, 1975 Northwest "Proto Toyhauler", 2004 Harbor Freight folding, still seeking my Airstream.