Imagine an accident in which the RV comes to a complete stop very quickly (as in hitting a semi-truck that just pulled out of a side street right in front of the RV.
If the tow bar angles down from the RV to the Jeep, the momentum of the Jeep is going to try to go under the tow bar and raise the RV in the air - which it won't be able to do, so it will just stop more suddenly.
If the tow bar angles up from the RV to the Jeep, the momentum of the Jeep is going to try to rise up above the front tow bar connection and slam the jeep into the rear of the RV above the RV hitch.
My guess is that tow bar angle is of little importance regarding the damage to the RV from the collision (it's going to be totaled), but in the "angle down" case, the Jeep might have less damage.
YMMV
