We know the park--very nice place and owners as you said. We stay across the road at El Manglar, since when we arrived for the first time in Zihuatanejo more than 10 years ago Costa Bella was full. (They had about 10 spaces then--before the appartments) so we dry camped in El Manglar Restaurant parking lot. Next season they started their RV Park.
IF the restaurant is still open (they usually close for a few months in the summer) the food is the best on the beach. If they are there tell them Arturo says hello!
For local information we can also recommend Zihuarob's website and forums at
http://www.zihuatanejo.netEnjoy Zihuatanejo. We won't be there until December.