This is a common problem for sailplanes stored in trailers in the desert.
Some ventilation is the key to keeping the moisture from building up inside the container.
A solar powered vent on top will help -
http://www.westmarine.com/webapp/wcs...classNum=50678
Place it at one end and put some screened openings low down at the other end.
It can be used in conjunction with one that is wind powered -
http://www.westmarine.com/webapp/wcs...classNum=50678
A white painted container will also help, and definitely make sure it is pack rat proof...
