I think the strangest part of this story has to be that you are spending your time and energy, two days in a row, from several different angles/locations, to take pictures of some stranger's vehicle, and then post it online.
Maybe they intended to stop for an hour, and then their child got sick, so they rushed him to the hospital and left their RV there. Maybe they know something you don't about the rules and regulations of the area. Maybe the occupants of the RV were kidnapped by a drug cartel. Maybe they just have a crap-ton of money and don't care about getting a ticket. No matter the reason, it's irrelevant.
If I noticed a strange man photographing my RV for two days, I would call the police. I think you should probably just go enjoy the beach, and leave it be.