Can't promise you either. I spent aboout six days in the Coconino National Forest, just on the northwest outskirts of Flagstaff back in April. Reasonably nice weather, but did have to run the furnace for two nights. The high desert gets a little chili at night.
My TT is an older Jayco, and it sits a bit low, too. (In process of switching to a Coachmen 5er.) Roads are unimproved, and could easily be called trails. It was dry while I was there, and I figured if it rained, I'd be stuck there until it dried up again.
It's not bad, but expect to NOT have a campfire at all while there. (Or generator running, or charcoal grill, etc.) We had burn bans while there, and I'm sure it's just as dry in September.
Overall, a decent way to camp.....Roger