I can confirm that hot glue guns do NOT work for door panels. The glue only lasts for a little while before separating again, which is why I've done mine twice. 2nd time around I used a 2-part epoxy.
1998 BMW 328is Shooting Brake
1966 Pontiac GTO
2007 Subaru Impreza 2.5i 5-door
View my photos: Caught in the Wild