Easiest route in Yellowstone Park for 1st Time RVer

Get a copy of the Mountain Directory West (there is also one for the east). Use it to check your planned route to see what steep passes and grades are on that route and change routes if necessary. If you do come in from the south you will go through Grand Tetons National Park. I highly recommend you spend a couple nights there. Then it's only about 60 miles to Yellowstone. Have a great trip.