I used regular plastic inserts for concrete screws from home depot and they work great. not on the panels but for the rear vents and side markers.BTW, old thread revival. I tried pretty good steel nutserts on the side panels holes. 2 were loose and spun.
What a huge PITA to remove! I would not recommend, the interior tin is too thin to really get a good grip
with nutserts. I still looking at/for alternatives now.