I have a 9200 Polar Cub on my 11.5 foot Bigfoot TC. So far, it has done a great job. I can't see you having any cooling issues with the Coleman Mach 8 cub.
I can't see any problem with the voltage. My bet is that you are plugged in to 120-volts. For your information, the voltage can fluctuate for many reasons. I have ran my Polar Cub on voltage as low as 109.
My bet is the smaller A/C will be more efficient than your big one. It will not cycle as often, and do better at removing the moisture from the air. Bigger is not necessarily better with A/Cs.
I am not in the A/C profession, but have a pretty good grip on the basics. I selected and installed my Polar Cub in 2005 and usually run it on my Honda 2000 generator when camping. I have ran it in campgrounds with varying voltages.
Wayne