I just wanted to add regarding trailers: if you enable swing drive (and maybe twist) on a spawned physics cosntraint actor, which is onyl available via blueprints (and probably code) (its nto in the settings) and locking all the angular setups except twist I left to 1 degree you get a MUCH more stable setup.
If I could get it even more stable I could almost make my project come true! Makes me really wanna dig into the code after final exams and start learning the UE4 API.