'They' make a bit for your drill that does a great job on sheet metal.
It is basically a circle cutter, where an arm attached to a center shaft allows you to move the carbon steel bit out to whatever diameter you want. It makes a nice, clean cut, too. Goes through aluminum like butter and is suitable for auto body metal. It's perfect for dash gage/meter installation.
I've been planning to do the flush mount to my '86 CJ-7, and when I do I'll pick up one of those bits at the Depot. And I WILL use oil (A-Ganger) though that bit is pretty easy to sharpen.