I'm going to tell you the way I see it. The UP in mid September to early October is stunningly beautiful. The crowds are sparse. The weather will be very cool at night; could get down to 30°±. The days will be very pleasant 60°s to mid 70°s. In my opinion, your "no freezing weather" means you want to miss out on the absolute best time to visit the UP. Your RV has a furnace, being from Washington I presume you have a variety of jackets. It's really a no brainer, it's not like it's going to be 40° below.
