we purchased 3 of these dehumidifiers for our trailer a few years back. I can now say we cannot live without them. They are about 30$ to purchase but getting into a bed in a trailer that is not damp, to me it's worth every single penny. We were purchasing the stuff that comes with it but discovered that that can get pricey so we purchased a 20lb bag of calcium and use that instead. The premise is simple, add calcium to the top and it absorbes the water in the air and collects it down below to be dumped later. My trailer is as dry as dry can be and no more watery windows either.