I agree with Rogue.
If your Montana is equipped with Generator Prep - the intended design primarily focuses on installation of an LP fueled Onan like pictured here. The Generator Prep can be identified by a tin shroud on the curb side of the front cabinet that serves as a heat shield (shown in pic below), an automatic transfer switch (Iota) located on the firewall behind the battery, and a 4X4 box with two red push button breakers mounted in the blue face plate (shown in pic below at very right lower corner). If none of that is there, then you don't have prep and would be steps ahead just going with a portable generator.
