I agree 100% with MPond.
I am a big reservation person as I want to know I have a place with a site I want and not spend good time trying to figure out where I will be staying. Would rather be photo shooting, hiking, etc.
With your rig, you should be making reservations IMHO.
Having lived in CO for 8 years and traveled it much more I have found that the time after Labor Day can have lots of tourists - it is beautiful fall colors in the mountains, etc.
We used to call that time the season of the newlyweds and nearly deads !