What if you get the H/FP/PP Barracks OL in the water anyways, would the Barracks OL just sink into the water or something? Would it even be pushable in the water?
This is exactly my question. I have come across a few exceptions in VCS, namely the Sentinel XS and Bobcat from this mission, the Boxville from "Domo Arigato Domestoboto", and most importantly; our beloved Jetmax. These vehicles are Heavy, but before storing them, they don't sink underwater. They do after you take them out of the garage though
That said, the H/FP/PP Barracks OL does sink after successfully storing it in the garage, but I don't know what happens if you throw it in the water during the mission.