I have an old 4 pint milk carton cut in half and half filled with rock salt, works a treat at capturing the mosture, when it is saturated I just bring it into the house for 24 hours. It will never collect so much mosture that it leaks water.
Home to black Alfa Romeo 159 3.2 V6 Q4 ,green MGF VVC and red MG Maestro T16.
MG - the friendly marque.