I had squeaking from movement between the cab and the coach on my 2018 Thor Four Winds so dropped the upholstery and found that they used Styrofoam blocks in the upholstering. The bolts were loose so I put star lock washers on them and reinstalled them - after resealing the entire area where the cab an coach met because you could see daylight and feel wind blowing through there. Because it's so easy to drop the cab ceiling upholstery to get the access you need I went ahead and reassembled it after resealing it and putting some rubber between the Styrofoam and the cab metal so I could see whether that would do the job. We drove it about 10 miles and it was quiet as a mouse, so we'll see how it holds up. To reseal it I pulled all of the bolts and ran a heavy bead of siliconized acrylic caulk (not to be confused with silicone caulk!) between the sheet metal of the cab and the fiberglass of the coach, and then reinstalled the bolts that I had added star type lock washers to. I didn't set out to fix any air drafts but man did sealing that gap make a big difference. Just another example of good products suffering from poor workmanship. It's all fixable though.
Here's a photo where you can see the screws around the cutout and the white Styrofoam sitting up on top of the mats.
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