Old Faithful?

We liked Fishing Bridge. It has full hookups. Not sure of the size restrictions.

Old Faithful is not ground zero in the Park. That said you have to go there and see that. The Old Faithful Lodge is worth the trip in itself. Plan on having lunch or dinner. Just take in the setting and send yourself back a hundred years. Most idiots see the geyser as just another tourist attraction like an animated stop at Disneyland. It makes me almost cry when they clap at Nature's majesty.

With a 45' 5th wheel and the truck you won't fit in anything in the park. You'll need to park outside the national park. West Yellowstone is your best bet.

Our 40' motorhome and car fit in a few of the park's campgrounds but you're too long.

As mentioned, Old Faithful is not the only place you should zero in. There are many awesome sites through the whole park. Drive every road in it for a good experience.

Don't forget about the neighboring park - Grand Teton Nat'l Park. It's a beauty and is completely different in looks and things to do.

Each national park in the country has an awesome web site of things to do, road information, opening/closing dates, campgrounds, special alerts, etc. Check them out.

https://www.nps.gov/yell/planyourvisit/index.htm

Here's a live web cam of Old Faithful. You can watch it erupt every day before you get there. :)

https://www.nps.gov/features/yell/webcam/oldFaithfulStreaming.html

... and Grand Teton Nat'l Park:

https://www.nps.gov/grte/planyourvisit/index.htm

As previously mentioned, there is no campground near Old Faithful - depending on your definition of "near." The closest gateway community is West Yellowstone, and Grizzly RV Park there has pullthru sites that will fit a rig that large. Very nice CG, only a few blocks to the west entrance of the park. As mentioned previously, expect to do a LOT of driving inside the park. Distances between features to see are not large, but lower speed limits, tourist traffic and wildlife jams make it a relatively slow ride. There is MUCH more than Old Faithful to see in the park; plan to spend several days.

We stayed outside the park west of west Yellowstone because we were visiting other areas and the Caribou-Targhee National Forest. We stayed at Buffalo Run RV Park & Cabins, 3402 US-20, Island Park, ID 83429, buffalorunrvpark.com, (208) 558-7112. Nice small park with room for a big trailer.
Bill

We like Fishing Bridge RV Campground because it is in the park and has full hookups. You can check the web site to insure it can handle a rig of your size.

I don't know of any CG in that area. The Hotel is the only lodging there. You need to be ready to do a lot of driving no matter where you camp in YNP. The park is only a little smaller than Rhode Island and Delaware combined.

Here is a list of the CG in the park: YNP

Only two have any services.

Commercial parks in West Yellowstone would be best.
Madison Campground in the park would be closes, but not many sites for your length.