My car came to me with fiberglass replacement door pockets. No idea how long ago they were upgraded. The passenger side is fine, no warping and the pocket lid fits nicely.
But despite being fiberglass, the driver's side pocket had bowed out in the middle and no longer supported the lid properly.
Note that it looks OK at both ends, but not in the middle. Rather than replace the pocket(s) again, I decided to look for a way to pull the pocket back into shape and reinforce it.
What I found was an old bronze-color shelf bracket support. Extruded aluminum U-channel with slots in the face.
My idea was to place this inside the pocket and bridge the bowed out section using a screw or two to pull the pocket straight. I planned to mount it inside about 3/4-1" down. Note the gap between the pocket and the reinforcement.
I drilled two holes in the pocket, and used a couple of black pan head sheet metal screws to screw through the pocket into the reinforcement. You can actually see where I put the screws if you look closely at the picture above. I mounted the reinforcement with the open side facing away from the driver, and ran the screws into the existing slots in the face of the aluminum. That made the drilling easy, as I didn't have to drill the reinforcement, nor be overly fussy about measuring the holes. Then I tightened the screws to pull the pocket up snug to the rigid reinforcement.
It worked beautifully. The pocket again supports the lid nicely, and the black screw heads are nearly invisible in the brown carpet. I'm pleased with the result. It was a cheap fix, should be permanent, and not visible at all unless you open the lid (which I almost never do). I used less than half of the aluminum upright, and plan to keep the other half for the passenger side, if and when.
Thought I'd share it here. It's not a concours type fix, but for a regular use car like mine, I think it's a good fix.