Set NPC door in trailer park?

I believe that NPC doors need to be interior to a building unless you have a mod that allows otherwise.

However, I am puzzled as to why your lot type is set as an Apartment lot. Is this as viewed in Edit Town? What that does (again, without mods) is engage the town's roommate service so that up to 7 NPC roommates will be assigned to the resident household living in the one usable unit. This designation is for the Uni style apartment lot and is based on the concept of dorms, ported to a homeworld.

For a Late Nite style apartment lot with the callbox, private/public room markers, and NPC doors, the more typical choice for lot type is Residential-Regular (or Ownable if your actively played household is to purchase it). Again, unless you are using an apartment mod that requires something different.

Thanks Igazor! I ended up having to just change my lot to a regular lot and delete the markers, reset the doors and I assigned my roommates to sleep on beds in the different homes on the lot. It's not the same, but I think it's as close as I can get to my Sim having neighbors in the trailer park. I appreciate your help!