small electrical charge on truck camper frame

I have a interesting situation where every once in a while, not often I can feel a small electrical charge on my truck camper aluminum frame or door latch. I believe it is only with the 12 volt system. Not the 120. On my last trip I pulled over and sure enough I could feel it when opening the door. At first I thought I had a metal sliver in my finger tip, but nope it was electrical. I got back in my truck and drove on further and it hasn't returned. But I could actually feel it on my truck body also at the time. Traced down my line from the truck battery to the camper and found nothing there. Any ideas how to find this culprit.

This is my 1998 Lance 980 truck camper .

Thanks