For $350 to $400 you can get 2 100 watt panels, controller, mounts and wire from panels to controller. Add another $50 ish for wire from controller to battery and other small parts. 200 watts is a good starting point and will keep your batteries charged for the most part.
Roof is about the best place for panels as there is no messing with them and there always doing the job. As for holes in your roof you have to remember that your trailer already has around 100 holes in the roof for vents, ac and antennas so whats a couple more.