The sleeper berth is subject to inspection under MCS regs just as every part of the commercial vehicle. During the MCS inspection the officer has legal grounds to look into and inspect the sleeper berth. A warrant is not needed. Any illegal items found during an MCS inspection subjects the driver to whatever legal sanctions might apply, ie, you can be arrested.
As a long time driver (35+ years) I'll agree to an extent. However, an officer would need at least some level of probable cause to inspect to that extent.
I got into a stop several years ago down in Tennessee at a scales, while driving a flatbed. It went to the extent they brought a drug dog to the scene, and walked him around the truck. When they got to the driver's side door, the officer started to pick up the dog, and I asked what he was doing. He said he was going to put the dog into my truck to "look around", and I refused to allow him to, I locked the door and slammed it.
The officer called his supervisor to the scene, and when he arrived, he asked me what my objection to the dog searching my truck was. I told them I didn't bring my dog to their house and put him in their bed, and I wasn't going to allow them to do that to me. If the dog alerted to anything on my truck, there were tools in the side box, and I'd gladly allow them to disassemble the entire truck if they wished. The supervisor agreed to that.
This was back in the Keith Bissel days in Tennessee, when the PSC was his little kingdom, and he allowed preferred treatment to companies who contributed to his campaign fund, and harassed any out-of-state driver.
The only probable cause the inspecting officer had was the fact I have long hair. I'd have allowed the officer himself to physically inspect any area of the truck, but I'll not go for a canine crawling all through my sleeper, if I wanted a dog in there, I'd have my own in the truck.
Yep, I know I could well have been "stuffed and cuffed", and taken to the judge to sort it out. But, I still maintain the mere fact that I hold a CDL does not mean I gave up my constitutional rights.
You might have the legal right to inspect anything on the truck, but I hear vehicle inspection officers complain that they don't get the proper respect from drivers. Respect is a two-way street, and Lord knows I've dealt with way too many over zealous inspection officers over the years, and gave them much more respect than I have received in return from many of them. If I treat you with respect, answer any question truthfully, and am complying with all regulations, one would think I'd get treated with respect in return.
Sadly, that's too often not the reality of a commercial vehicle stop. Maybe people skills could be included into the training for such officers? Yes, I know, you've got a tough job. Mine is no bed of roses either. I've got cranky shippers and receivers to deal with. I've got a dispatcher calling me hourly wanting to know EXACTLY when I'm going to be at a specific location, it matters not the weather conditions, traffic conditions, or how I feel that day. I've got vehicles cutting me off and slamming the brakes for no reason other than they obviously think I can stop a 80,000 pound vehicle on a dime. And then I get the vehicle inspection officer from hell to deal with when I'm following all the laws and regulations. And I'm supposed to just stand there and take the abuse?