I would check the sidewalls for delamination, and inside the MH for leaks, if no delamination or leaks are found and the roof underneath has no soft spots when you walk on it I would not worry why the roof was replaced. The PO could have backed into a tree limb or something. These roofs are very thin not like a boat hull or FG front cap. As far as 105k miles the PO used it and if it was well maintained and the price is right asked to see the maintenance records. If everything else checks out and you like the MH make him an offer.