This is photo of your main TV. I really doubt it is a digital one but the previous owner may have upgraded tv's...
There is nothing special about the TV to being a built-in one. This is just a standard TV like you find at WALMART and runs from 120VAC. When you look at it you will see what you need to get it to be a digital type. In addition to being digital when camping off the power grid you will always have to use an small 300W INVERTER or so to produce 120VAC from your battery setup.
You may not want to change it out but you will miss out on the great quality of TV the new digital HDTV give you now... The analog type using the digital conversion will pick up the local digital TV just fine but the quality wont be as good as it could be. It will be the same quality as what you will see when connected to CABLE TV coming from a camp ground when using the digital conversion box...
Always fun getting something new and making things like you want them to be... Enjoy it...
Roy Ken