well, I would say for the trailer, this winegard box would be a good one. It cost a little more than the wally world ones, but the ability to power it without the wall wart or hardwired 110 is a major +. It would figure since winegard are the TV folks for Rvs.
You could hack into one of the hard wired ones, but without a schematic to be accurate and the time it would take to do it, I would rather spend the extra 10 bucks.
I have not permanently installed it yet. I have to cut a slot in the glass on the wall my TV is on, and hardwire in the DC-DC converter. I want to make it look nice and haven't decided on the woods my cabinets will eventually end up being.. I want the trim to match. At the same time I am in there, I need to install a 110 outlet in the same area for my mini microwave
.. it will be a days work in a tight space. I want to do it all at once to get the foul language over with :-P