LOL, I always put it OVER, and my Rockwood trailer towed just fine.
But my wife would put it UNDER and on the way home once we had an accident!!! It must be directly related to that fact and not due to the guy swerving onto the shoulder to avoid someone he thought was in the left lane...
On all my other RV's I submitted to wife's wishes and put it Under. Then I also didn't have any accidents ;)
In our park model our dispenser is vertical storage and faces the user, so over or under becomes left or right. I prefer left (over) and wife likes right (under). /rolleyes