What you see at quite a few campgrounds is that a trailer has to be "self-contained" which means that it has a regular bathroom and gray/black and fresh tanks. Some places add, "no port-a-potties allowed."
Many people believe that no small trailers are self-contained because very few are. What such campgrounds are probably doing is protecting against fouled water being dumped, often on the ground. Unfortunately, that is what a lot of people do.
In the case you mention, they may figure that they are taking care of the problem by not having to deal with people trying to get in who claim that they are self-contained when they are not. You could call such a place in advance and maybe they would look up your trailer and believe you (but people can have Escapes with no bath.)
Cathy. Floating Cloud
"Live in the sunshine, swim the sea, drink the wild air.... "