They all work but I like maps.yahoo.com Enter starting and end points and it will map your route and give you driving directions and distances. Estimate how far you want to drive before stopping. Double click on the map (next to but not on) the mapped route to center the map and zoom in to that point. Adjust the map scale. Enter "campgrounds" (or anything else) in the find a business box. Find one near the interstate. You have do play with the program a bit to discover all of its features. The nice part about all of this is that it does not limit you, for example, to just KOA or Passport America campgrounds, so you get a lot more hits.
Happy Camping! ///// Richard D.
2006 4x4 Ford 250 SD / 2007 Flagstaff 827 FLS
One very patient wife and one furry child who travels with us. Forty-two years of trailering and camping, and I still have a blast.