If you are trying to mount 4" Trucklite type lights, they take a 4 1/2" hole. Although a drill press would be the safer way of doing it, wusually don't have to option us putting it in a drill press. We use a Lenox bimetal. They can be bought on eBay for $16 including shipping. Item No. 230631333187. You will also need a mandrel. It takes a good 1/2" drill... The slower the speed the better. And it is just like drilling a any big hole in metal. I kind of tease the throttle towards the end because they can grab when you break through.
