I bought a relibilt french door that is 5″ too tall than the opening. I was thinking I could cut 2 1/2″ off the top and bottom. I was going to dig out about 3″ or so of the foam from inside then cut the same size piece of pressure treated lumber to glue in side the door where I took out the foam. It seems like this would work. The doors have a metal skin on the outside.
Mike