* The vehicle's sticker: Look for a sticker on the driver's side doorjamb or inside the glove compartment. This sticker will list the GVWR.
* The owner's manual: The owner's manual should specify the GVWR.
* The vehicle's title or registration: Sometimes this documentation will include the GVWR.
Without access to one of these sources for a particular van, it's impossible to give a definitive answer. The GVWR could range from around 8,500 lbs to potentially over 10,000 lbs depending on options.