I'm not familiar with MH mirrors, but for threaded inserts in the existing holes there are threaded nuts that apply kinda like pop-rivets, don't know what they are named though.
2000 Winnebago Ultimate Freedom USQ40JD,
ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG 11B5MX,Infantry retired;Good Sam Life member,FMCA." My fellow Americans, ask not what your country can do for you, ask what you can do for your country. John F. Kennedy