Mark,
Your question regarding A/C's has been asked over the years almost as much as "Which came first, the chicken or the egg?" Marketing Prevost Conversions over 20 years, I can tell you from experience that "everyone" is different. What appears to be cold to one person, may still seem hot to the other person. I've been driving down the highway in about every conversion out there, and have been hot, look over at my wife, and she's covered up with a blanket. Now that we're getting older, she's hot (hot flashes) and I'm covered up with a blanket.

OTR A/C was developed by Prevost for a commercial application (seated buses) hauling a bunch of passengers that produce a lot of body heat. It's almost an overkill in a (2) person conversion, however, if you want to hang meat inside your coach in AZ. in the summertime, it'll get the job done.
It's wonderful, and if your generator fails, or A/C fails (roof or cruise), you have the OTR as a back up. Down side, it takes up storage and horse power (when running).

Three A/C's is "very marginal" in humid, southern climates. The technology of inverters in the newer coaches and battery power can allow you to run several a/c's without starting the generator. Then, you have some converters that do their own OTR system with an a/c compressor 1/4 the size of the Prevost OTR. Then, you can get into the cruise a/c's in comparison to the roof a/c's. All converters use to have cruise a/c's and I think it was Angola or American that put the first roof a/c on a Prevost in the early 90's. It was a slow evolution, but several other converters followed five to seven years later. Other converters opted to stay with the cruise a/c's. Then you get into serviceability, noise factors between each, etc. and so on and so forth. I agree with Donnie, (3) roof a/c's is not enough (at least in Florida this time of year).
Steve
Parliament