I have done this. You'll need a pair of "diplixer's"
Diplexer's combine the sat and cable signals, then on the other side break them apart again. On the outside connect the combine side (labeled in/out in the pic) to the camper, then the satellite and cable to the respective connections. On the inside remove the AB jumper and hook the diplexer combine side to the A port, then the uhf to the B port and finally sat to satellite. There you have it, one line and both satellite and cable. There's other ways to configure the inside part, but this is the general idea.