Two years ago we drove from Kelowna to Calgary around late-October. We were not in an RV. Temperature was 15 C in Kelowna, 10 c in Calgary but below zero in the mountain passes.
Highway enforcement officers were in the mandatory truck turn out/brake check areas checking for tire chains in larger vehicles.
We encountered a few flurries along the way and one real winter storm around Golden on the TransCanada.
I think the general consensus from the replies is that your plan is a little late in the season but could be done.
It really would be a great trip but for me personally the enjoyment factor would be significantly higher in September/October vs November/December