If anything is bouncing enough to damage the hydraulic system then SOMEBODY needs to stop prerunning the Baha 1000 towing a boat..... even then I think the hull would be busted up way before the hydraulics had any problem at all..... maybe if the boat got rear ended by a car but then you'd have bigger issues.
It's not because you should be afraid of the drive falling, but rather that the bouncing down the highway could damage the hydraulics.
My dad knew someone who lost chunks of the lower unit while there were traveling to and from the lake because the hydraulics failed. With the hydraulics out, what happens if a line breaks or leaks......... Gravity wins! For my boat its a risk I am not taking and a just throw a strap on while i am at the back strapping the boat to the trailer. But I know I have a hydraulic leak somewhere, because I am always refilling the hydraulic tank every few trips, so I'm at a higher risk factor.