Best place to mount a spare (without a rim attached)

Monkeyman....Yo can buy a steel wheel for your spare and it will fit all three positions, front, outside dual and inside dual, without issue. If you have space under the coach, you can make an arm that bolts/pivots on one side, slide the spare over the arm, use a floor jack and bolt the other side of the arm to the frame. Many have done this under their coach when the frame is an open type.