Your fix was interesting. Did Chuck say if your original installation was or was not to the clearance specifications published in the Norcold installation manual? Also, how close to those specs are you with the new piece of sheet metal installed?
On a previous rig I checked and rebuilt the rear of the fridge compartment to EXACTLY (within 1/16" or less) the measurements specified by Norcold and did not find any improvement in the Norcold's cooling ability. I'm wondering if Chuck has found a solution something that few before him have found, or if your box is different from the many who have not been able to find a fix that works.
I tend to think that your Norcold is somewhat unique, as I can't see how this fix would have caused a refrig such as ours that worked for 2+ years and suddenly stopped working despite the compartment rebuild and 2 Amish cooling units.
Regardless of how it happened, I'm glad your man came up with a fix that worked for you. I wish you continued good luck with it.
Pigman & Piglady
2013 Tiffin Allegro Bus 43' QGP
2011 Chevy Silverado 1500
SMI Air Force One toad brake
Street Atlas USA Plus