Stainless Steel Lid

I just picked up a stainless Steel Drum the other day, I'm so excited. The only thing wrongwith it is that it came with a lid with no bung holes. Does anyone have any suggestions as to how to but and exhaust on the lid with out warpping it? i thing that I want to put a 3" or 4" exhaust tip.

I thing and 3" or 4" hole will but and exhaust on the lid with out warpping it.