In addition to RV Park Reviews (our first stop on the 'net when looking for a site), there are a handful of apps that help. RVParky and Allstays are very handy for short notice, what's nearby decisions.
Just a note on RV Park Reviews: Watch for campgrounds that have few reviews. You can't count on the accuracy of such reviews. Any good reviews were probably made by the owners or their family, bad reviews by the competition.
I look for a park with >10 reviews within the past 6-12 months with an average rating >7.5.