You can pick up a True RMS inverter in the 300 watt range that will run the tv off battery power and your alternator will keep the battery charged. The TV only draws 40-80 watts depending on size and the DVD player is down under 30 watts. But dont buy one of the cheap switched inverter or the TV will hum and you will get static lines. Dont get one that is too small like under 200 watts because the TV will draw a surge current when you first turn it on before it settles to its running current and dont get one that is too big over 500 watts because it will have a greater parasitic draw even when your not using any appliance. Your going to pay $150+ for a good inverter but it will be worth it in gas savings and peace and quiet while the TV is on.
You could also get a big inverter wired into the coach but you will pay big bucks and need a sizeable battery bank to run it.