I could see that. It would depend on the type of vehicle, to be sure. My truck is old enough that it has door handles and mirrors mounted on tubular steel but many newer vehicles are much "slicker" on the outside. In a shallow river or other body of water that was waist deep or shallower you should get enough leverage from your legs but in a water over your head it would be an issue, for sure.
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“I'd rather have questions that cannot be answered than answers that can't be questioned.” —Richard Feynman