While on the road, you see lots of minivans being used as toads.
However, most of them are not four-down-compatible without modification.
Most folks seem to like the various Remco modifications--axle disconnect, transmission pump, or (for rear-wheel drive minivans--if there are any--a driveshaft disconnect).
Remco has a good web site that will give you lots of good info--but none of the changes come very cheaply.
Yes, you can tow minivans four-down -- but not out-the-door.
Cheers and Happy Travels,