I tried to add box collision and set collision to BlockAll(or BlockAllDynamics). This workaround does not work if such primitive overlaps vehicle physics body! Vehicle just jumps into the air. Even if it does not overlap, it could cause serious bugs in physics for big vehicles. Try to set scale to 2.0 for the root vehicle mesh(also don’t forget to change size of wheels in wheels blueprints) and see what’s will happen(depends on a position of collision box, it could jump to the air or bend forward or backward). I have such a big vehicle, so your solution is not works for me. 
Given the above, I do not think that’s a good idea to mark this question as a resolved.