The first time you have to replace an AC unit due to low voltage damage you will wish you had one. I recommend this company, http://www.progressiveindustries.net/ , They offer a lifetime warranty and have excellent customer support. I would suggest spend a little more and get the EMS series which protects from surges, over voltage, under voltage, miswired connection, and does a checkout of the power available before it is ever applied to the RV. If you plug in and there is a problem with power there will be no power to the RV that could damage it. Especially nice if you have 50A service and the pole has a bad neutral which will put 240v on the 120 circuits. It won't turn on.
Some like the portable, mine is hardwired. That way if there is a problem at the pole, with my power cord, or the connection on the side of the RV it won't turn on.
My 2 cents worth.