Gas stops along route to Yellowstone.

As far as what you can get into, you might see if you can find a copy of "The Next Exit." You might find one in a truck stop or, of course, an RV supply store. They highlight gas stations, RV parks, etc., that are (at least mostly) RV-friendly. We have found ours helpful. It does need to be as up to date as possible, though - a several-years-old used one might not be quite as good.

Crossing MO on 36, you will find accessible stations in Monroe, Chillicothe, Cameron; and St. Joseph will have plenty.
I think Chillicothe has a Walmart, but not sure if it has the gas station.

I try to use Flying Js for the Good Sam Discount but with that said... there are a number of decent APPs for locating fueling stops. Just check your App store and hunt around the truck, camping, and RV apps.

Wherever you can get into, and the price is not a rip-off. We used to look for WalMarts because of the discount when using their credit card. but they have discontinued that so better to use wherever and pay cash.