Usually...if OTHERS at the park are getting cable and you are not...8 of 10 times it is your hookup cable...or the cable connections inside the coach. The other two times it is the campground cable connection.
If you are SURE your cable is good...run it through a window and attach it directly to rule out a "house" wiring problem. Still no picture...check your assumptions about the cable...do a continuity test with a voltmeter on the wire and the shield.
If all is good...chances are you need a longer cable since the one in your campsite is kaput!
(continuity test procedure for coax: How to check coaxial cable with a multimeter | Courage Kenny Handiham Program
) Essentially...hook up your multimeter to ohm setting and touch the two leads together...you should see close to 0 rather than close to infinity! Now put the probes on the central wire at both ends of your cable...you should still see close to zero. Finally put ONE probe on the central wire and another at the "screw" side of the opposite end of the wire. You should still see near zero or you have a short.
All good? Call your park host!
Just as a note...I'd add that you can get a lot of small tv's in thrift shops cheap. A 19" flat screen NEW goes for $99 bucks these days at Best Buy and Wally World . Not only are these good for the picnic table...but they provide a very convenient way to check for a good park signal!