Best big rig campgrounds around east side of yellowstone

Check for availability in Fishing Bridge. They have some spots that will accommodate big rigs.

It's pricey but when you are looking at an hour drive each way to get in and out of the park each day, it's worth it.

The nearest one with electricity is a Federal campground called Rex Hale, about 16 miles east of the east gate into the Park. There is another fed campground with elec. at Wapiti, about 22 miles east of the Park entrance.
Inside the Park, Bridge Bay campground has a good dump station and water, but no elec. and you definitely need reservations for a rig as big as yours.
If you want to explore Cody, WY before going on to the Park, the Ponderosa RV Park is your best bet (IMO) and again, reservations are a must.
Or, you can go through the Park to West Yellowstone which is tucked up next to the west Park gate, and there are several rv parks in town to choose from..with reservations.
Our preferred choice is about 15 miles south/west of the West Yellowstone, called Henry's Lake State Park, which has it all. View, hookups etc.

We stayed at Yellowstone RV park in Gardiner with our 36 ft 5 wheel and a medium duty truck and it was right above the river giving fantastic views of the boaters floating down. It was about a couple miles from the entrance to the park and easy to get in and out. The only drawback was the entrance to the park is a fairly steep decent down a dirt road, everyone does it but a bit intimidating when first being seen. You will go down and back up in whatever rig your in. Not a resort, but worked well for the week we were there.

Each year we traveled from Detroit area to Las Vegas to Tucson Az then on to boloxi and Fl. We stayed at or near casinos every time many were just a small charge if any and a lot of times being a returning customer we got free meals and other comps. Casinos have the best security, wifi, and entertainment. Michigan offers great camp grounds in the upper at the casinos there.

Not any great options East, we have been there 6 times in the last 12 years, in West Yellowstone you have Grizzly (our favorite) and 2 KOA's - Yellowstone is huge and on the east side its 140 miles round trip from Cody just to get to the park