If you have a cable that goes to just one TV, or one that connects to a switch assembly to select what each TV gets it signal from, then you already have what you need. If you presently have a single connection for cable that then goes through a signal splitter to send that signal to two TV sets, you will need to find a way to connect the dish receiver in between the outside connection and that signal splitter. If you do put the dish receiver in that position, it will also mean that the dish will feed the same programing to both TV sets.
In most cases, where an RV has the split signal to a TV in the front and one in the rear, that splitter is not easily accessible. In such a case the easiest thing to do is to run a new cable from the outside to the place where you wish to put your satellite dish receiver and then connect it to one TV, or install a splitter at that point.