Ridged Insulation:
Testing the ridged insulation we put it in water for like a weak and I have also pulled it out of foundations where it was exposed to water all the time and it was still good. I have used it in full size boats with no problems

Here is a web site of one of the products that stats "it's practically impossible for it to be penetrated by moisture"
http://www.owenscorning.com/around/i...s/foamular.asp

hope this helps