Stanczak...
Unless it's broken or disconnected via a klll/disconnect switch, I'm quite sure the 12-Volt system in your coach is hot (working) as you're travelling down the road, so a 12-Volt TV, plugged into a cigarette lighter, for example, should work just fine as you're driving down the road.
Your TV will need to have an input jack that corresponds to the output jack of a laptop or stand-alone DVD player - most commonly RCA or HDMI jacks. Most modern flat-screen TVs have HDMI, VGA, S-video, Composite and RCA input jacks. Older flat-screens may not have an HDMI input. Most modern laptops have HDMI and VGA jacks to output to a flat-screen TV, but many older laptops only have a VGA jack - no HDMI. Few, if any, modern laptops have RCA jacks. RCA jacks are most commonly found on stand-alone DVD players (the little round red, yellow and white jacks). So, as you can see, it really depends on the age of your equipment and how it's equipped.
I'm sure I don't have to mention this but for the sake of safety I will... Please ensure that the driver can't watch the TV while on the road. I've actually seen this happen. It's not only illegal, it's VERY unsafe.
Kev