Cannot run A/C while at highway speeds

So, a partial update on the status of the investigation. While we were in Wyoming, one of the EU2000's started to burn considerably more oil than it should have. It was created a definite blue smoke screen when started every morning. So, on a business trip to Arizona, I came across an Onan 4kw Microquiet with only 290 hours on it. Had the guy start it up and run it under a load. Ran like a champ with no apparent oil usage. So, long story short, instead of trying to "fix" the EU2000 storage box I have to address a probable vacuum issue, I'm going to redesign the whole thing to handle the new Onan. Including sound isolation and vibration dampers. Plus, with a dedicated muffler, I plan to run the exhaust stack up the side of the rear stairs. This should eliminate any potential odors AND reduce some of the noise. My goal is going to be to get the noise level down to the point where you have to be within about 20'-30' of it before you even notice it. A lofty goal to be sure, but possibly doable. I'll keep everyone informed of my progress and may even be able to post some pictures. But, remember, we're staying comfortably in the high 90's to low 100's. May still be a while before I take this one on. Thanks for everyone's help. I think with the right setup, this will solve my problems. Plus, my wife can start it without ever leaving the trailer!

Scot