On my 07 Meridian (sister to journey) the mirror does somewhat the same thing. If it is the whole mirror part that moves there are screws that can be tightened. By removing the protection caps the set screws can be seen.
If its the wind that moves just the mirror, mine does that also. I have tryed to move the whole mirror assembly so the wind may not catch the mirror. That seemes to help somewhat. I have no idea of the rod you are talking about.
Good Luck
Itasca Meridian SE 36g
Road Master Tow Dolly