1. Drag in some SCR_DestructibleEntity and add the compartment-relevant components to it (ControllersManager, VehicleAnimation, BaseCompartmentManager, ActionsManager, Rpl, VehicleCameraData) and configure them. I'm attatching a test entity so you don't have to do all this yourself.
2. If done correctly, you will be able to enter the compartment.
3. However, under these two conditions, the camera will instead get stuck in place, and you will not enter the compartment:
a) You are a client, not the server.
b) No one has tried to enter this compartment before you.
Also, if you get stuck, you won't be able to move, but the game doesn't freeze or anything, it's just that the camera is stuck and nothing happens.
If you are stuck and press Q/E, you will however for some reason get unstuck again, the animation plays and you continue to enter the compartment.
This issue does not occur if you are the server/in singleplayer, if someone else tried to get in before, or if the entity is e. g. a GenericEntity.

This issue is not critical to Reforger, but a significant roadblock to compartment modding for purposes like in test entity I am providing.
The test entity is a replacer for BenchStreet_01_Base.