We used to carry ours (radio's) in a briefcase, with a 500 watt Palomar right next to it, the antenna was welded to a pair of vice-grips which we clamped to the top of the mirror post on the pass. side on an old Fruitliner or KW and run 3500 miles and never missed a lick.
I dont know where length of coax came in either, I think once an antenna is SWR'ed to a particular radio, coax length wouldnt have much effect unless it was significant, but I dont know. I know we hooked up more than a few without checking anything and dont recall blowing up any radios, but I did check SWR whenever I had a "good" radio, I think it helps to have it matched if nothing else. One thing I remember, is a good antenna will always make a bad radio look good, and a good radio isnt any better than a bad radio if you have a bad antenna. Once again, get the tallest antennas you can live with, and put them up as high as your comfortable with. Most OTR trucks have them up where they just clear freeway overpasses. But they also have them up front, and with that long trailer most of their radio power is behind them. On a Bus, if they were mounted in back and set to clear 11-12 feet, or at least as tall as your AC's, you should be good.
We are running a short antenna in our coach, just barely above the AC's as you point out, it is a magnetic jobbie, if the need arises, it can be laid down if we have to do it. It is also hooked up to a 500 watt Palomar which on a good day, gives it a range of about 35-37 miles, which is okay in my book.
Remember the good old days, KKV-5865.