With the hinges coming along so nicely, I thought I would take another look at the back door of the main body. In my initial rough assembly, I noticed that the back door didn't fit too well. It was too small.
I took the old back door, and traced it out onto a sheet of styrene of the same thickness. It would make for a good starting poing.
I cut the styrene out using some sharp scissors, but left extra room around one side. This would account for the material I needed to add in to make it fit better.
After a few minutes with a couple of files, I got it to fit pretty well. It's not perfect, but when I paint it up, some thickness will be added. That should iron out any kinks.