With a 120W solar panel, the controller may be more necessary. It depends on your battery set-up and how much you enjoy keeping an eye on the voltmeter.
If you have 1, 12v battery, a 7A charge (which would only happen with peak Sun angle) may be a bit much
for several hours unless the battery is ~50% discharged.
If you have 2, batteries (either 6v or 12v) the need for a controller is less vital because (essentially) peak charge rate will be ~3.5A per battery and will only occur for a few hours per day with a permanently mounted panel. If the batteries are in good condition, you need only check the voltmeter every few hours to make sure that the battery voltage does not exceed 15V. I would recommend disconnecting if you see 14.8V.
Basically, that's all that a controller does anyway.
I have a 160W array and my batteries will top-up around 2:PM on a Sunny day (with normal usage). I would think that your batteries may top-up by the end of the day........all things being equal (I have 2-6V golf-cart batteries).
I actually recommend that people do this (go without a controller) when they 1st start out with solar. It helps the user be more aware of how the panels operate.
Having said all that, if you leave the panel hooked up while the camper is stored outside, a controller is essential.
As for wiring........I have my panels mounted on the rear shell with a short run (~14') to my batteries which are located in the rear of the camper. I use 10G marine grade wire and it is adequate.
Your batteries are located on the front of the trailer. Because of the long run to the batteries, I would recommend using the 8G wire that is available from the solar companies. Although you could get away with 10G, I would not recommend it. If, in the future, you decide to add an additional panel, you will absolutely need the 8G wire. There is no sense in buying and running the wire twice.
As far as controllers go, there are as many selections as you have $. I have this simple 20A PWM controller:
http://cgi.ebay.com/20A-PWM-regulato...item3f05edcd28
The MPPT controllers will give you about 10% additional amperage while charging for ~100%+ more money. In my book, that's not a very good return on investment for these small arrays. I would think that the extra $ might be better spent on a larger panel..........but that's just me. If you take that extra $100 (or so) and put it into a larger array, you could go from 100W to ~150W (a 50% increase in output).