Even though it doesn't get wet , there is always dampness in the air.Having the soft top off is too much air to have.You want the windows cracked just a little bit , not too much.If they are open too much , it defeats the purpose of having them cracked a little.A good example would be to cruise a junk yard and look in some of the vehicles they have.The ones with no doors , or even no windows will be pretty moldy.If you find some where the windows are just barely cracked , you won't see anything , unless it was wet to begin with , like a leaky floor or something and the carpet was soaked.Then theres too much moisture all ready , and if you had the windows all the way up , your truck would be all fogged up in the morning as it has no where to go , plus the extra water in the carpets.