Using a regular hole saw blade on thin metal is frightening! As the saw pierces the metal they catch and usually tear things up pretty bad. Carbide faces hole saws will work with a bit of care, it must be the smooth faced type like the forth one pictured in the like below. Even with that type you must go slow and careful. On a few applications where I had room I glued a block of wood to the back side that works well. The other option is to mark out your hole then drill a series of holes with a small bit just inside the line, then clean it up with a barrel sanding bit in a fairly high speed drill. Again take your time and be careful.
Phil
No matter what your beliefs are "GOD BLESS AMERICA"
Fully retired marine tech near 60 years in the biz.