Roger,
Are you staying at Grizzly Rv Park in West Yellowstone? Nice place.
From Caspar, its best to head on the two lane (26) to Shoshoni, and then turn north to Thermopolis, and then to Cody and west towards the East Gate of Yellowstone.
Your GPS may want to to head north from the Fishing Bridge, to Canyon Village and to WEst Yell by way of Norris and Madison jct.
Take it from us, once you pass over the Fishing Bridge and get to the intersection, go south towards West thumb and onto Old Faithful, its quicker to get to Madison jct and West Yell.
If your coming to Spearfish./ I would recommend heading north out of West Y on Rt 191 towards Bozeman. ( 90 miles) At the FourCorners, there in the Gallatin valley turn east on Huffine Lane which is actually West Main st thru Downtown Bozeman and on the east side of downtown is I-90.
It will take you ever so long to drive back thru the park to get on the roads to Spearfish. what ever you do have fun and safe travels.
Jim and Chris
2001 Featherlite Vogue XLV 2 slide with Rivets-current coach, 1999 shell
Previous 22 years,
We have owned every kind of Prevost shell but an H3-40