I think the concern with the "legalities" of ownership/rentership have overridden the idea of common courtesy.
If you are at the beach and lay out your beach towels and have your cooler, etc. in close proximity, while it's not illegal for someone to walk through your things, it is considered rude.
Same with a campsite. It may not be illegal to walk between my RV and the picnic table at my site, but it is rude. As some campers don't mind (and some even appear to enjoy the "camaraderie"), asking first may result in your being able to reduce your walking distance. But don't get mad if someone says no to your question and respect their wishes and walk around. And don't just do it without asking. Show some respect for others.