Sounds like what you really need is a digital tv. I have found a great selection of 12 volt digital TVs. In fact I just bought one last week. I live off the grid too. I haven't found any 12 Volt Converter Boxes or I would have bought one. Hell I'd even buy you one. Wish they made such a thing.
On the bright side. . . This new TV is awesome! Love the HiDef picture. Wouldn't have gotten this with a converter box.