Re: Introduction...
Hollis, as with everything, you will get the best results if you do your part.
What I do is decide where I want to go and enter the info into Microsoft Streets and Trips to get a route. It is set up to indicate where it suggests I spend the night (based on desired start time, end time, speed and breaks). Then I look for PA sites in the area. within a mile or so of the route and within an hour of the suggested layover. Sometimes there isn't a PA site which is located within that zone; often there is at least one (in the southwest at least).
If multiple ones, I look at price and amenities; here is also where you can verify any restrictions. If none, but one before or after the zone, I see if my plans can be moved (leave earlier or later in the morning, drive a different speed, use a different PA site the night before or after). Sometimes there will be one on an acceptable alternate route (once there was none along the interstates going by a city north and then turning southward, but there was a nice one SE of the city on state highways, about the same distance. If there is just not one which works, then I use a non-PA site. Between Tucson and Central Illinois, it is rare to use more than 1 non-PA site. Between central Illinois and Boston, I think it was about 50/50. Not that there are not sites there, it is just that they tend to be further from the interstates and/or have more stringent restrictions.
Once I have the route mapped out and the parks decided on, I call for verification and reservations. Some places like them and some won't accept them from PA members (they don't want to turn away any full pricers). If I can't get a reservation, I make sure I have a backup site nearby or other plan. Obviously, a place with 7 sites is more of a risk than one with 70.
I tend to 'travel', so generally 1 night per place is plenty. On only 2 occasions did I spend more than 1 night at a PA park and neither one gave me any problem with staying 2 or 3 nights.
Keep in mind that if you can use 5 PA nights in a year, you are likely making out like a bandit (2 or 3 and you may be breaking even).