I've been stopped once, about 7 years ago, driving my motorhome. It was an interesting experience, so I figured I'd share what happened and how I approached it.
First of all, it was dark, and caught me by surprise--I had no idea why I was being stopped, but had regularly seen cars being searched along that stretch of I-40 (Shelby County, TN).
I had never given much thought to a traffic stop, but as I was stopping, the first thing that popped into my mind was how I absolutely wouldn't want to approach a high RV window if I were a police officer, where there would be no way to see what was going on inside. I had a mid-ship entry door, so his approach from the passenger side wouldn't have been any better.
I had a switch on the dashboard for a side-facing floodlight. I turned that on immediately on getting stopped, and exited the RV calmly. I walked to the rear of my rig, and waited for him to get out of his car.
I was allegedly stopped for going 71 in a 65 zone (just before the speed limit went to 70). I had been having trouble with the speedometer drive gear on my GearVendors overdrive, and knew I couldn't have been going that fast. I also had a laptop on the dashboard with a GPS that had been logging my position and speeds all day--and told the officer as much. It was a relaxed conversation, and he dropped the pretense for the stop and explained that they were looking for drug trafficking. After a few questions about where I was going, and whether anyone else was inside, he asked if he could search the RV. I gave him a few conditions (like being able to watch, to be able to stop the search at any time, and that everything had to be put back as they found it), and thought it would be somewhat amusing given the hidden spaces that would be hard to search. That resulted in a quick end to the stop and I was on my way--without him ever asking for my driver's license or registration, setting foot inside, etc.
Bottom line, I think, is that the approach put him at ease, and things usually turn out better that way. I had no intention of allowing an invasive search, but he didn't have to know that.