I’ve been wracking my brain on this one too. A project I’m working on requires exactly this, large vehicles that are essentially “micro-levels”. Unfortunately my experience thus far is limited to Blueprint scripting and I don’t have enough experience with C++ to properly tackle the problem.
One approach I thought might work is if you could attach an actor to another actor and then have the “attachee” (is that a word?) simulate all it’s movement and physics in the parent Actor’s local space. Essentially the new Parent actor becomes the child actor’s world and it can only interact with the parent and siblings.
Probably easier said than done though.
EDIT: I just spotted your post here: Custom CharacterMovement component - need help - C++ Gameplay Programming - Unreal Engine Forums. Again, this is pretty much what I’m trying to do as well but not having any luck.