I am cooking for 18 on Thanksgiving. Getting nervous about trying to cook everything on the actual day. I would like to cook about 15 lbs of mashed potatoes either the day before (if you say there's a way!) or the morning of Thanksgiving. How do I keep them from drying out...and how do I reheat them? I am actually thinking of using disposable lasanga pans in order to fit a lot in the oven. P.S. I don't need a recipe for the mashed potatoes...my husband's come out absolutely delicious!!!! Thanks for your expertise!!