Greg,
The interior wals are covered (for the most part) by plastic panels. I've seen different colors on the Defender (tan, black, dark grey). Here's some pics.
As you can see, the floors are sheet metal and have strips of non-skid on them. The cockpit floors are the same. The doors have plastic panels on the interior that conform to the inner surface of the door. If I were you, I'd leave the doors of to show more detail. Just my
worth.