I agree with you somewhat Robin, flying appliances and cabinets in a rollover would not be not be good in any scenario. However, if you happen to be in a bad enough situation to roll the bus your chances of living through it have decreased significantly anyway.
I'm going with the floating floor in mine and taking my chances by driving very prudently and remembering I'm in charge of 36,000 rolling pounds within my ability to control. Therefore going 60 mph is plenty fast for me as I'll be in no hurry to get anywhere.
That will allow me to not put screws down into the metal floor and allow numerous access points for moisture to wick it's way up into my bus.
Besides, unless you have something very heavy sitting in the middle of the floor, which is highly unlikely since it's in the path of the very small walkway of a bus interior, there is no reason why items up against the walls cannot be bolted to the walls and secured that way.