The bottom of our cabover area's floor is cutout part-way (so you can raise up out of the cab seats to go back to the coach) and mates securely to a matching cutout in the cab's steel roof. In fact in looks very much like the cab's steel roof helps to support the cabover - in addition to the aluminum struts in the cabover walls themselves that are of course extensions of the aluminum joists and runners used in the entire coach area's walls and ceiling.
How can our cabover area "bounce independently" if it's bottom rides right on - and is attached to - the Ford cab's steel roof? Especially how can it bounce relative to the coach's sidewalls that are the same piece of vertical material making up the cabover's sidewalls?
I'm almost about to use the word "impossible" relative to any cabover up/down movement separate from the Ford cab roof itself. I've never seen our cabover "move separate from" the main coach structure ... and I sure hope that our whole coach never moves relative to the main chassis steel frame beams that it's bolted to and that support it.
However, we did once own a Class C in which the cabover floor was separate from the cab's intact steel roof. There was 2-3 inches of air between the outer surface of cabover floor and the cab's steel roof (just like in a truck camper). I suppose in that case, the cabover could sometimes bounch a little vertically separate from the cab, but even then we never experienced any leaks in the cabover sleeping area.
What I don't trust to not need leak over time are: The five forward facing clearance lights in the cabover, and the forward facing cabover window seal for those of us unlucky enough to have one. When our Class C is in uncovered storage out in the back yard, I'm very careful to keep it parked it in the shade so that the sun cannot shine on the cabover window or on the clearance lights. The sun's UV rays are a killer to just about any sealing material - so shade or a roof covering are essential to keeping an RV's roof areas sealed up tight.
We also long ago installed vent covers over our roof vents so that UV rays wouldn't cause the plastic crank-up vents to crack and leak water. These covers over the vents also help to keep water away from the screwed-down and sealed vent frame itself so as to help prevent leaks in that area.