We use the "Kilrock" granules and containers in our house next to the windows to help reduce the condensation on the windows overnight, it's about £7 for a 2.5kg tub, we get through a couple of tubs per winter. I have used them to dry out cars in the past and it does work well, certainly worth a go, but definitely put the container thing in a bowl - the car I left mine in was not used all the time and the container was overflowed when I looked at it the next time!