I take it the "looking inside" was looking through windows and, if the door was left open, through the open door. That's legit. Interior stuff visible in that manner is considered "in plain sight" and no search warrant is needed for that look. If anything in plain sight raises further suspicions, such as a weapon or contraband, that lets them go further... enter the rig, look more closely at stuff.
I agree that there's nothing unusual about an RV parked at a public park. The number of people who responded is unusual, though.
Just last week I had an incident... far more mild than the OP's, fortunately. My cargo trailer is unusual, a molded fiberglass body produced primarily to make TTs, but I bought an empty one with just 2 small side windows and the small window in the rear entry door. I sell/deliver books and stuff in schools, been doing it for 25 years.
So I walk out of a school building with my hand truck and 2 bins of merchandise on it, and halfway to the parking lot I notice 2 guys hovering around my rig. They're looking at my trailer and my SUV, checking the license tag, looking in the trailer's windows. They have handguns and stuff on their belts... they're off-duty cops working their second job as security guards for the school district. They look mildly concerned. Well, I walked up pulling my hand truck, with a smile on my face, and said, "Any questions, comments, curse words?" :) They looked at me and asked who I was and what I was doing, still on alert a bit. I identified myself by company name, and said I'd just made a delivery to the office, and I opened the door and started putting my bins inside the trailer. They could see in the trailer quite well at that point... all my display racks and bins of product... and their antennas switched off. They started asking casual questions like, "Who makes these trailers? It looks cool."
I can imagine how things would escalate if I walked up looking grim, worried, nervous, acting defensive. Not saying the OP was doing any of that... I wasn't there. Obviously with that many guys, they were already on high alert for some reason. The two I encountered were just doing their jobs, being cautious. But I guess both of these situations are signs of a general heightened security stance and greater vigilance currently taking place around the country. I can't say it is misplaced, either, considering all that his happening in the world. Not much we can do about it. Just gotta make sure we have nothing to hide, and act friendly and transparent and patient. (Note: by transparent, I do not mean give them permission to search... just act innocent and willingly give them all documents and reasonable info they ask for.)
