We went this year in our truck and camper in September to both places, and did not have reservations for our stays. A lot depends on what you expect to do, if you are avid hikers, or more inclined to drive and then walk about a bit.
But first.. both places have parks that are and perhaps with your service you may qualify for discounted rates. That would help. Gros Ventre in Grand Teton would certainly be a good spot to land and from there you can drive about with your toad. It is totally non hook up except for the park employees, but they did talk of that changing.
September is packed with tourists that figure the same as you.. we were overwhelmed with the numbers. The RV Parks are best booked for a bigger rig like yours. We had to be settled by about noon to get a spot in some places. It is really busy.
The best times we had were in the outside parks away from the National Parks. Some of the smaller ones still open were truly lovely places, quiet and peaceful, and with the pick of the prime sites in that season.
We stayed two nights in the Tetons, then headed east and went to the Longhorn Ranch and RV Resort in Dubois. What a beautiful and peaceful spot! Didn't hurt a bit to see a fisherman carrying his catch back from a time on the river. We went to Thermopolis and toured the dinosaur museum there, certainly wished I had spent more time there. A huge hotsprings for touring and for a swimming break there.
On to Cody to the western museum there, again worth a double day for a good visit. We went out to the State Park along the lake and stayed two nights.
From there, into Yellowstone... oh boy.. drive to see everything, busy busy busy, we stayed in two different parks, both with no reservations, and wild panic between 6:30 and 8:00 AM with people running about trying to secure sites that were vacating that morning. We checked the Weather Radio and left to the west with snow approaching that night.
In two days we were at a NFS site along the Crooked River near Bend, Oregon. How peaceful and lovely.
If you have to see with your own eyes, by all means visit the National Parks. The sights are truly impressive and wonderful. But if you want a relaxing journey, and are equally impressed by smaller venues, down home warm and fuzzy food, and local events, then enjoy the journey there and back, but be prepared to stay outside for the most part, and take the roads less travelled.
Mike
2012 Winnebago Impulse Silver 26QP
2005 16.6 Double Eagle
2018 Jeep Wrangler JK
previously Snowbird Campers,
Triple E Motorhome and Fifth Wheel