There is great boon docking outside of the organized campground area.  Follow your GPS to 44°35'52"N x 111°25'18"W.  At ~6,500 feet, the views of Lake Henry are amazing.  There are 15-20 spots suitable for RV's (of any length) plus campsites.  It's a great location, only about 20-30 minutes from West Yellowstone and the entrance to the national park.  We could have stayed here for days!  

5-bar coverage on Verizon.