Usually the 120VAC HDTVs I have seen at the stores that has the 120VAC Transformer modules is usually a 15-19VDC source required. This has worked great for me in the past. My on-board converter/charger can have as high as 14.4VDC on the 12VDC grid so having the 15V-19VDC TV voltage requirement was great.
They used be very common things to have in the older TVs but these days most of them have built-in power supplies and only work off 120VAC...
When you go to the stores just look behind all of the TVs they have on display and I bet all you see will not be using an external transformer module. Very rare to find one that still uses them.
For me the HDTV was only half the problem. The other things like DVDs, SAT RCVRs, Cell Phone and Computer chargers, etc will probably also need to be fired up when you are camping of the power grid. I ended up with a 600W PURE SIGN WAVE Inverter to handle all of the things we wanted to have ON when camping off the power grid. We normally use right at 300WATTS being pulled from our Pure Sign Wave Inverter so purchased one with double that output to be to able to handle anything else we might want to add to it...
It is all what you want to do
Roy Ken