Try to hit speed bumps straight on (both wheels over at the same time) and very slowly. If you drive over them at an angle (one wheel over slightly ahead of the other), your coach will rock back and forth, from side to side, especially in the back. Even going dead slow (creeping), driving over the speed bumps at an angle may cause the coach to rock enough to actually cause things to fly out of the upper cabinets! This is true with the small speed bumps, too.
This will also be the case if one side of your wheels hits a depression or pothole commonly found in some of the truck stop lots and campgrounds, the small bumps going up into driveways and parking lots, and the rain gutters built into the cross streets, especially in the South. Driving dead slow with frequent braking is the only answer.