If you cradle panels, you know that even cradle boards can warp.
Here is what I like to do:
I use "Hobby Boards" instead of the big one by twos. They are thinner and come in pine, poplar, and oak, at Home Depot, Lowes, etc. I like poplar.
Cut your boards to size of panel, glue and clamp. Wait a few hours.
also, purchase some aluminum angles......again; home depot, lowes, cheap. Cut them to size with hack saw.....easy. Cut half way thru then bend til' they break.
Now, place the cut aluminum on the inside of the cradle boards flush.
Use self drilling metal screws (the little ones) to secure the angles.
Stronger and lighter.