Voltage at campground low ??

I was camping at an older campground and it was hot outside. The campground was full and there were many large trailers and motor homes. As the day heated up I noticed that my AC was less and less efficient to the point that it would hardly cycle on. I learned by talking to my tech guy that when older systems like the one at the campground become overloaded the voltage drop can be alarming. I installed an inexpensive volt meter and now watch it when I am hooked up to a campground electrical system. I have seen that the voltage will drop as usage increases but this doesn't always happen. Yes, a poor connection at the post can cause issues but I believe that the overall capacity of the system is the real culprit. To start with, get a volt meter that you can simply plug into one of the outlets and then watch it when you are out.
The more expensive systems are better but you might want to start simple and see.