All route planning is done on MS Streets & Trips. S&Ts shows many CGs but it does not show all of them. Lots of county parks & small town parks are missing. RV Park Reviews is another great tool but it too is missing many of the smaller CGs that nobody has reviewed. Adding a CG on RVPR is cumbersome so there is not much incentive to add a CG when discovered. Allstays is very good for finding CGs but usually there are few reviews unless it is a big CG.
The directorys are good but how much can one trust the ratings?
Bottom line is the information is out there. You just need to find it.
As a rule we do not make reservations. It has been very very seldom that we have been turned away. Call it the thrill of uncertainty but there is always somewhere to stop the wheels & get some sleep.