Solar panels are basically sold as a comodity these days. Watch for a good deal on a dollars/ watt basis. The larger the panel the better that ration will be. The largest panels, like are used on homes, measure 78" by 40" and produce around 350 watts. If you can fit one of those it will be your best deal. The next size down measures about 66" by 40" and produce around 300 watts. These are also generally a good deal. When you get smaller than that you're more into "RV" sized panels but the cost per watt goes up.
I would put on one 300 watt panel if you have the room. I wouldn't bother with anything less than 100 watts.
Forget about running the AC on solar. You would have to spend a fortune on panels and batteries. The weight and space requirements would be outrageous, particularly on a trailer that size. I install off grid solar systems for a living. Even off grid homes with thousands of watts of PV don't typically run air conditioning.