Red,
We often travel much the way you seem to and the simple answer is that there is no simple answer...?
In our experience, there are three sources to work from:
RV Parky (free)
Allstays (App 10$)
Street Atlas with the Discovery owner's overlays. (SA 40$ overlays free)
All three are varying degrees of incomplete.
The top two can be run on a smart phone.
We actually end up overnight where I have planned about two-thirds of the time.
*I didn't list RV park reviews because they only review real RV parks and not Walmarts, casinos and Cabela's. (edited by Matt)
Matt