sealing openings and equipment in outer walls.

Quick question, I've been making holes on the outside panels of my van, using a drill and self taping metal screws.

What do you guys use?

I tried a grinder (heats the metal and the paint changes color and starts to crack and flake off)
I tried a jigsaw/sawsall with masking tape around the opening, since the shell of a van is made of 2 panels (inside and outside) the blade hits the other panel and kicks back or breaks/bends the blade

This is the biggest hole I have to make for my fridge lower vent.