The coax has 75 ohms impedance. The old flat twin lead is 300 ohms impedance. Newer TV sets typically have only the 75 ohm F-connector. Radio Shack and other similar vendors sell 75 to 300 ohm baluns. These little matching transformers will permit interconnection of the different cables.
Pics of a couple types are seen here: http://en.wikipedia.org/wiki/Balun
In the long run, you might get better performance if you can run RG-6 coax from the antenna to the amplifier switch and then to the TV. Unfortunately this is easier said than done in most coaches.