Do you ever plan on running a top again? If not, just convert to a pickup tailgate.
And cut that bastard out. Fill with steel. my 1/4 rotted out there two years ago, and I cut a big hole in it, and bent new sheet to go in there. You can get rid of the whole panel. The strength is on the inside wall, not the outside. I drove around for a while with the hole, and my tailgate didn't rattle, or in any way flex the body with out the metal there. It did, however, look terrible.
Oh, yeah, and flipping finish your truck.
Baby Beast- Mini Truck in progress