Sprinter conversions (factory and home-crafted) are the common default answer, as the model has been around for a while. The more recent Ram ProMaster isn't as nice, but it's a lot cheaper for a similar age/mileage vehicle, and it's 4" wider inside. 4" doesn't sound like a lot, but it's enough to allow you to put a bed crossways that still comfortably fits a ~6 footer, something you can't do in a Sprinter.

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"They're made of latex, not nitroglycerin"