Yeah, put some 2x4s under them and make sure they're secured so they don't fall out, but I'd pull all the seats out, put some support under them, and haul them inside. Or use a trailer.
Though I have access to a pickup and plenty of trailers, I'd just borrow the flatbed and put them on it... I think that trailer weighs almost as much as your van empty, though. It's not light.