There's a RV park in Springdale, UT at the entrance to Zion. If the park campground is open (COVID-19) then you would fit in Watchman campground in the park itself. The free shuttle stops nearby. If the free park shuttles are running by Sept/Oct they will stop in Springdale, also. You don't want to take Hwy 9 east out of Zion to Hwy 89 - tunnel restrictions and steep uphill. You drive down the center of the tunnel and the NPS closes traffic so you can do it. There's an extra charge. Read about it before attempting - Zion Tunnel. You could do it if you disconnect the Jeep and drive separately. Instead, take Hwy 9 west to I-15 north then take Hwy 20 east to 89 and south to Hwy 12 east to Bryce.
On 12 to Bryce there is a short tunnel but absolutely no problem driving it with your 40'. We've done it often with our 40'.
Zion is an extremely congested park as there is only one road in the park which dead-ends and then you return the same way. Therefore, they use shuttles and typically don't allow your own car. I don't know how it will be by Sept/Oct if the virus is still going on. With only the shuttles it's very tolerable but if the shuttles aren't running? Right now with limitations on how many can enter it's not pleasant. Hopefully by then they'll have it figured out.
From Bryce take Hwy 12 east to Capitol Reef Nat'l Park - lot of RV parks in nearby Torrey.
Between Bryce and Capitol Reef on Hwy 12 a stop midway at Escalante would give you a chance to explore along Hwy 12 with your Jeep. Awesome drive on Hwy 12 but few pull-offs. If a hiker ask the visitor center in town about easy slot canyons to walk such as 'Spooky'.
Then take 24 east and north to I-70 for a short jaunt to Hwy 191 and Moab. Many parks here. Awesome Jeeping!! Go the Visitor's Center in town by the grocery store for lots of helpful information and maps. Close to Moab in Canyonlands Nat'l Park is a beautiful State Park - Dead Horse Point. Bring a full tank of water. That's where we stay if not boondocking in various places.
From Moab take 191 south to 163 at Bluff to Monument Valley. This is a Navajo Tribal park so no 4-wheeling. Stay on the roads. Many stay at Gouldings RV at the entrance. You could easily drive your Jeep on the circular rough dirt road through the Monument. We did. Or there are tours to be taken. Be warned that you'll get dusty on the tour .. they're in the open.
You could also work in Grand Canyon North Rim in your circle tour. Entrance is on Hwy 67 at Jacob Lake, AZ. 89 or 89A will take you to it. The park closes mid-Oct to camping, restaurants, etc. but they keep the gate open for a look-see. Be sure to do the walk from the national park Lodge out to the point. It's short but beautiful along the Rim.
Beautiful fall colors on the aspen trees. There's a pretty national forest service campground called De Motte at the park entrance. We've stayed there... no hookups. Just south of De Motte is a good , flat graveled forest road on the right and if you drive only 1/2 mile or so you'll begin to see many very nice boondocking sites to stay. The national park is redoing their campsites this summer so they might make more bigger rig sites. Check their web site or call.
If you're into animals of all kinds, especially dogs and cats, there's a terrific no-kill facility in Kanab, UT on 89 to tour called Best Friends Animal Sanctuary. It's in a beautiful red canyon setting. Best to call beforehand for a good tour or you can walk the grounds on your own. I recommend the tour. There's also Coral Pink Sand Dunes State Park at Kanab. You won't believe the color!
Depending if you do Grand Canyon and then on to Zion or vice versa, the best way would be to get to Fredonia, AZ just north of Jacob Lake on 89A and then pick up AZ 389 west which becomes UT 59 taking you to Hwy 9 and east to Springdale/Zion Nat'l Park.
Also on 89 is Glen Canyon Nat'l Rec Area at Page, AZ and from there you could tour Antelope Canyon via a tour only. Waheap RV park is overlooking the lake.
Each national park has a wonderful web site giving you up-to-date COVID-19 closures and openings, special alerts, road information, things to do, etc. Check them out.
I'd recommend at Least
Zion - 3 nights; more if you're a hiker
Capitol Reef - 3 nights
Moab/Arches/Canyonlands area: 1 week
Monument Valley 2 nights
Grand Canyon North Rim - 2-3 nights
Glen Canyon Nat'l Rec Area - 2-3 nights
This is a nice circular trip but you'll need to move to each place. The parks are too far apart to base camp.
Of course, you can add more nights but these are the minimums to plan on. Two months could easily be filled!! Enjoy.... favorite places of ours.