I have had a mini-split since I rebuilt my 16' Scamp
years age and I have been well pleased with it.
The heat pump is quieter than most if not all roof top units, but maybe not the the window units fitted in various places.
The smallest mini-split would be in the range of 9,000 BTU and that would be large for a 13' Scamp
Lots cheaper would be a window unit, but where to install it is a question.
I bought my unit in a spring sale from Johnstone Supply at wholesale price. I also rebuilt my frame and extended it about 18" to install the heat pump and increase the stability and reduce the tongue loading.
Also there is the question on where to mount the inside air handler.
Would I do it again? The answer is yes I would for MY Scamp project, and if you are handy it would be one answer.
If you are handy a small window unit might be an answer also.
I installed the heat pump to eliminate the need for an separate heater, but the Scamp with really no insulation is not a 4 season camper no matter what.
The AC is powerful enough to handle hot weather, but the cold will creep up through the floor. (The heat also creeps through the walls as well, but not as noticable).