Cleaning Snapback Hats

I buy and sell a ton of vintage snapback/ trucker hats. I find most of my hats at yard sales. And while the ones I find are usually in great shape, they aren't always very clean. Often times they are hats that have been sitting in a closet or garage somewhere and have collected lots of dust. So, I have to wash them.
You can not just throw these hats in the washing machine. That is a sure fire way to ruin them. You can add them to the washing machine if you first put it in one of those plastic doo dads meant for hats. I personally don't care for those, especially when washing vintage hats. Some of the older hats may be made with cardboard bills and letting it soak in water for any amount of time will ruin it. I did a little research on the best way to clean snapbacks and this is the way that seems to work best for me.