Give the braided cable a good pull, that release can be a bit sticky. It might help if you press in slightly on the TV to ease some of the tension on that latch. Once I got mine unlatched, I lubed it, and that helped.
But, why are you hooking it up direct to the TV anyhow? There should be a coax plate nearby with 3 outlets. 1 goes to the TV and the other two should be jumped together with a very short coax. It should be right next to the antenna 12 v power outlet. Wire your sat box where the jumper is, and the dish to the "cable input" jack most likely found at about eye level, near the rest of your utility hookups on the outside street side of the camper.
Of course, this all depends on your trailer and its options, but this seems to be pretty standard.
2014 Jay Flight 28 BHBE
2015 RAM 2500 6.4L HEMI, Tradesman 4x4, 3.73
Blue Ox SwayPro (BXW 1503)
Upgraded from an REI internal frame backpack and a Eureka 1/2 dome tent!