Try the trip planner at KOA.COM.
It is under the "Find & Reserve" tab now.
I find that the KOA banner takes some of the guess work out of finding a "good" place to park. You usually cough up an extra $10 to $15 per night for the quality. They aren't perfect. I found one that was barely adequate.
'07 Damon Outlaw 3611
CanAm Spyder in the "trunk"