The damper will only mask the problem. You have wear somewhere, or an alignment problem causing the death wobble. your safety is at issue here along with others, so fix the problem, don't just put a bandaid on it. When I had my Jeep many had the dreaded death wobble and the best cure was an aftermarket track bar that was better quality than what the cheapo Chrysler factory part. Your van doesn't have a track bar, but something in your steering or suspension has slop in order to cause the death wobble.
Back when I was a youngster my grandfather called it shimmy and that meant a trip to the alignment shop.