Worried about heavy satin wedding gown and hot and humid wedding day...?

My wedding is this weekend and the forecast says it will be in the upper 80's and very humid. I'm worried because the ceremony is outside and my dress is satin and weighs about 18 lbs and I am fit, but I still get sweaty really easily. Any ideas on how to stay cool or to avoid sweat dripping down my back in front of all my guests??