If you're taking I-80 you can take 287 at Rawlins into Teton Nat'l Park.
If you're ready for a night's stop at Lander, WY, take the time to go through South Pass City a neat ghost town on Hwy 28 not far out of town. We've stayed at Sinks Canyon State Park but there are a couple RV parks in town.
This way you avoid the massive traffic in the town of Jackson if you would have taken 191. Once you're at a campsite then you can take a day to tour Jackson without the RV. Jackson also has some large grocery stores if you need to stock up and just south of town at Smith's the grocery/liquor store also has good prices on fuel. Once you get into Yellowstone, you'll only have W. Yellowstone to purchase food and their prices will be higher and the stores are tiny so not as much selection.
From Lander and when you get to Moran Junction the view of the Tetons is breathtaking when you enter the park.
