Installing lights behind the sleeper

I dunno if they make a 4" knockout punch. Probably expensive if they do but it would sure make a clean hole without possibly damaging surrounding sheet metal/paint.

 

Quick Google search shows Greenlee makes a 4" knockout punch for a little under $200. Greenlee's are good tools but you can probably find something from harbor freight maybe for a lot cheaper if you don't want to spend a lot.

 

Well you need 4 1/16 or so hole saw that or you need a diegrinder to ream it out a little

 

Knockout punch is a lot cleaner. I wouldn't use a hole saw. After removing sleeper interior you pop a small guidehole in it with about a 5/16 or so drill bit. Then screw the halves of the knockout punch together and tighten with wrenches until it cuts out the hole. You won't scratch anything or bend any sheet metal oil panning it or anything like that.