I put a new 13.5 Carrier Roof mount in my old Lance and it was so noisy and cycled all the time.I would never put a 13.5 back in a pickup camper.
That is the size on my 8' camper and it is about twice what I need. Each day, I actually open a couple of windows to make it run more so the moisture is actually pulled out of the stuff. If I don't, everything starts getting damp because of the short cycles. Luckily, I don't camp that often in the hot summer, and have found the trick to make it bearable, just hate wasting the electricity.
While the 5k may not bring the temp down to 70* in the camper during the day when the sun is shining on it, it will definitely make it bearable, especially at night when you are trying to sleep.
