The Sanyo's are living up to their reputation. Good for you. In spite of your installation handicaps the thing is doing a great job. Try setting it to 60 degrees and see how much it will depress the temp in the bus. You may only need 2 units and that would be a significant cost reduction to the estimated 3.
You want to see the AC really perform? Tape plastic over the windows and windshield(if possible). This should give you a better idea of the AC performance "after" you get the conversion more complete with thermopane windows and UV filters/reflective. Insulation and air tight windows are more important than a whole flock of AC units. I can increase the temp of a 30 footer by 30 degrees with a single 1,500 watt cube heater only because the coach is like a thermos bottle in terms of sealing. One of the old style roof mount AC units has always been more than enough in temps of 100 degrees. Get anal about sealing that puppy up tight, Dog.
Keep us posted. I live vicariously,