I hadn't really put a lot of thought into the "waiting on the vehicle to fill with water then opening the doors" situation. I spend 99% of my time in either my company van with the driver's window rolled down, or in my Jeep with a soft top.

In the shape the Jeep and its top are in, there's very little chance it would be airtight enough to keep the doors held shut for long if at all.

Plus the soft top means I have a pretty easy way out if I need it, just slice it open.