I have a dent in the left rear of the box of the truck. It is about foot and half from the tailgate. I tried the plumbers helper the plunger. It didn’t even move it.
If there’s no paint damage or creasing, check into one of those paintless dent repair places. I’ve been very satisfied with their results in the past.
I saw another video like that, except a small block of CO2 (GLOVES, PLEASE!) was used to cool the dent.