Thanks guys, I managed to get it off and all but 1x mounting location is broken off. I'll JB-Weld it back together with some new clips. There's no screws, just green sockets with square holes that snap into the body. Then green pegs with a rectangle base slide onto the tabs on the cladding and snap in. Looks like the "ideal" way to remove it is to pry the velcro away from the truck on the rear, then pry the clip free on the corner near the velcro, looks like the whole thing could slide rearward and not break any tabs or clips. Mine had tape along the top so you'd have to pull it away gently but that seems like the most reasonable way to remove it.
Once the male green pegs are removed (or what's left of them) the green female clips in the body could then be pushed out from the inside.