I have used cooking foil (weak and will need replacing regularly if you take the chassis out regularly) , adhesive copper foil (better, and the adhesive reacts to heat so place it and warm it with a hot air gun) and nothing. Nothing works great!

I was gonna say, yeah, nothing will work fine. I've been running my amp out of its cab for a few weeks while i tweak the insides etc. Not a single cycle of noise at present..

that being said, I'm sure there would be a situation where you'd want that shielding there; large club with lights etc nearby, also if you have a c-lator etc on top, that would induce noise without that shield.