The interior needs special work. From what I can see in the episode, the interior panels under the rear windows were removed along with the back seat, although I've read that only the seat was removed to install the full roll cage.
So, I had to remove the rear panel and totally rebuild it as the interior structure that the panel would normally cover. Was a 2 full day scratchbuilding job, daunting at first but well worth it in the end.
The carpet will be well worn and stained soon.