Rear View a Mirror a Repair

This will not be an easy or fast fix. You have a steel, square tube cage built around the driving area. The mirrors are mounted on the outside near the dash. The easy way, without tearing the whole side apart, would be to do what has been done for years when adding a receiver hitch or doing suspension mods to passenger cars with a square frame. Use a 1/8" or thicker steel plate on the inside of the wall with a bolt pattern of the mirror base. You may have to trim/fit to the dash wall area inside. Using a long 1/8" bit drill through the wall from the outside into the people tank area, keeping the bit as square as possible to go straight in. You will need 4 bolts long enough to go through the mirror mount, wall and the new plate. After you determine the bolt size, you will need some pipe or steel tubing that the bolts will fit through. Once you determine the tubing size, drill a larger hole through the wall for the tubes. The tubes should be about 1/8" shorter that the wall thickness. The reasoning here is the tubing allows the mirror mount to be bolted up solid without crushing the wall to the steel cage. I would drill the bottom 2 holes first, then measure the mount pattern, to see if the pattern will fit under the dash. If not, a reevaluation of the process must be done for safety and looks on the inside of the MH.