Did you go into the tv settings and make sure they are both set to receive signal from cable (and not set on antenna)?
When you say "hook up the cable", do you mean an actual cable-tv cable? If so, you don't need to crank up the antenna. And if you're getting signal from cable, you might not need to push the "signal boost" button.
If you're going with antenna, it might have to be rotated so it's aimed the right direction. I usually look at other RV antennas in the area and match their alignment.
Lastly, I had to go through all the cable connectors under the wall plates and tighten them up, not long after I bought the trailer. All connections were loose, and I had problems getting a solid signal. Might check that, too.
2011 Dodge Ram 1500 HEMI Quad Cab
2011 Jay Flight 26BH