Well, there's a couple of ways and I guess you're talking about running cable coaxial from the cable box (at the campground) into the trailer?
For a couple of bucks you can get a flat connector that runs either under the door or at a window. Because it's flat, you can close the door or window without degradation of signal.
Or for something more permanent, you could mount a cable hatch and have the coaxial in a cupboard, etc.
When I purchased my trailer, the previous owner ran the coaxial out the
electrical hatch....
Is this what you were asking?