Steve,

Go out w/ a tape measure and write down the distance to the tailpipe. This is the depth you can sit in if there aren't waves / water movement. Now, subtract how much you value your van. There's your answer. An extra 20min sucks, but I'd prefer not to risk losing the engine, or the entire van. Locally (VA), every time we have a tropical storm / hurricane a bunch of people lose their cars as they think it's shallow enough. It's not worth it.

BTW, if that water's moving much I wouldn't even try and cross. Once you get out there the van will easily be pushed with the current. That can make you lose the car - and you're life.

john