Alright, new problem...
I exported the interior as a Legacy Dif into the game's interiors folder.
I need to load this into slate, so I can edit the map from there. For some reason, the interior turns white when I place it, and I click the "Relight Scene" option, and this doesn't help. There are also walls in the interior that act like they're not there, and I can just walk through them. Also, theres a few holes (missing faces) in the interior as well...