Reinforce metal shed doors

I've recently had to move my shop/tool storge out into a small metal shed. I've finally got the roof sealed up enough that I'm not getting drips. Now I'm looking to reinforce the doors. The are just pieces of thin sheetmetal with a bend on each size and a sheetmetal U bolted vertically in the middle. They slide to each side on a track. When I got the shed, the door hardware had been lost(used shed/never installed.) I made some "wheels" to run in the upper track out of washers and bolts. The bottom of the door floats in a track at the bottom.

I would like to reinforce the doors both to lock the shed up and to prevent the wind from blowing the doors in.

I was planning on putting 5/8" plywood panels cut to fit inside the metal doors in. Problem is, The doors eac measure ~58"x 28" so I can only get one panel out of a sheet of plywood with a lot of waste.


Anyone have any idea on what else I could use? I can't make the doors any thicker because I've got shelves on one side and a workbench on the other with just big enough gaps for the doors to slide open.