WARM Pacific waters are not to be found in San Diego or anywhere in CA :) You can swim in the ocean but a summer wet suit is recommended even in Aug. As far as full hook-up coast campgrounds go I would look at https://missionbayrvresort.com/
If you are going to Roswell, NM (http://www.redbarnrvparkroswellnm.com/) you might as well drop down to Carlsbad Caverns and hit White Sands Nat. Monument as you pass by.
I hope you are planning a spring trip to avoid the 100+ temps you will find around Roswell in summer.
