Re: Boxes won't fit.....help please...
If the choice is to not use the box or shim it, then shim it. One way that I might do that is to drive a flathead screw into the 3/4" thick edge of the box. Screw it in enough until the screw acts as leg to stop the rocking. If you then want to block the gap, screw some scrap to the outside edge of the warped box to close the gap, It may not be pretty, but it will be functional.
--- Victor Hugo - "Common sense is in spite of, not the result of, education.”