Mine is 41.5 feet, yours is 40.5 feet. When they get that long, the rear over hang is so great, even the slightest bump causes the rear to bounce and bounce hard. A tire hitting a 1 inch deep hole will cause the center of the trailer to slightly move. But the end may move 6 inches, and forcefully too.
I have a rear bedroom with the closet across the entire rear. On our maiden voyage, the entire closet inside collapsed, shelf on the floor, cloths on the floor, and 4 tiny holes in the walls where screws use to be holding a hundred pounds of cloths and bedding with g-forces probably twice that of normal gravity, up and down. Lesson learned. Long story short, I ended up rebuilding the entire closet ... from the floor up ... literally, and all the support is now from the floor, not the walls.
I did the same thing when we installed the washer-dryer too. I rebuilt the shelves they sit on from the floor up. I learned my lesson from the collapsed closet.
In your case, with the refrigerator in the very rear, it is going to get an extreme amount of bounce and g-forces up-and-down at every bounce. The length of the rear is just too far from the axles. The law of the lever will prevail. All you can do is think creatively how to secure the refrigerator in place, to keep it from moving, and perhaps do some creative re-wiring so things don't come unplugged.
Unfortunately, this is a problem with all of these 40 (plus) foot campers. The rear takes a horrible beating. You'll just need to rebuild and strength any moving items. Avoiding bumps in the road is impossible. Rebuilding your camper to strengthen everything is a must.
2019 Montana High Country 375FL
2014 Chevy Silverado Duramax, 6.6L Dually