I have added a 3 ac and recommend it 100%. My front unit was a 15,000btu and the rear was a 12,500btu. Here in the Texas heat and humidity the set-up was marginal at best. I could only keep the house about 85f-88f regardless of what I did. Add the Grand Kids or visitors in an out and it was just hot.......
3rd 15,000btu unit went into to the roof vent spot and I wired separately with stand alone breaker box. This new unit is primarily only for when camping not travelling. We also never dry camp so now I just have 2 shore power cords 1 for the coach overall and 1 for the 3rd ac which is a 30 amp connection. Works great and recommend highly. The 3rd unit is also a heat pump for the winter. I have gone from 2 tanks of propane per season to 1 in now 2 seasons.
ctc