While you can get away with connecting directly to the 12V system, our DC system spends considerable time during the day up to 14.8V. So I just use inexpensive DC-DC converters similar to these: http://www.amazon.com/Parts-Express-12V-2A-Converter/dp/B000KGKFA4 (this is only a quick example, and only good for 2A - there are others more suitable for your application at similar prices).

We have them for 5-12V equipment like TV's and for 14-20V stuff like computers. I cut the wires from both ends and install them in-line with fixed mount equipment, and use the mating plugs for portable equipment.

Your other option is to get an inexpensive DC-AC pocket inverter and just wire that in-line permanently. These have very little standby current draw (almost immeasurable), and the power conversion losses for something like a TV will also be immeasurable.

Mark