If you find you don't have enough watts, you could consider a smaller a/c unit. Here is a unit that is only 9,200 and only draws between 1200 and 1500 watts as opposed to the 2500 to 3000 watts for the 13,500 or 15,000. They also make some 13,500's that have a low amp draw but you'll have to search for them.
Small RV Air Conditioner on Sale - PPL Motor Homes
Here's another and it's specs:
1/3 hp compressor motor, the most powerful in the RV industry today
Running Watts for Cooling - 1225 to 1450 Watts
Approximate full load amps - cooling - 11.1 amps
Evaporator Air Delivery on high speed - 200 CFM
Dimensions: 44 2/25" L x 32" W x 10" H
Weight: 92 lbs
Optional 5,600 Btuh heating element to take the chill out of cool mornings.