I'm leaning toward that too, Don . Also, the focus on numerous fuse pops and just replacing them over and over!
I have seen the problem be as simple as the incorrect bulb in the system to direct short from either chaffing or corrosion in the socket.

 

certain Jeeps were notorius for chafing of wiring on tailgate door, from frequent opening-closing. Your license plate lamp is on that door. might start there?

 

Had the same issue w/2008 HHR. replaced blown fuse and it blew ag
ain right away. installed a new relay, new fuse and everything works normal. #68 relay #69 10a fuse.. relay first, fuse second.
Hope that helps

 

Looking about 2 days 4 this same problem... found what look to be reflectors on the bumper were actually parking lamps! Found lamp above exaust wire harness melted so the fuse only blew when the car warmed up.hope this was helpful.