During our RV days, we always stayed at SPs if there was one close by where we were going. In 4 years we only went "commercial" maybe four times. Our trips were all WA and OR, mainly the coasts. Both states have websites with layouts and photos.
The only problems we ran into was with the older parks, which had narrow internal roads and sites at 90 degrees to the road. Even with our 32' Class A, some of them needed very careful maneuvering.
Being retirees, we planned our tips to leave home after lunch on Sundays and on long trips we stayed over the weekends after arriving on Thursdays. We rarely had problems finding a site on Sunday thru Thursday evenings, as those folks who worked during the week weren't there.