Here's the recipe/method we used at Girl's Camp last month.
Best way to cook corn for a crowd. Ever.
Cooler Corn (for 350)
A Bountiful Kitchen
175 ears of corn, husked and broken in half to yield 350 pieces
coolers (we used two 165 Quart coolers they were about 1/2 full of corn, you may use smaller coolers)
About 2 1/2 to 3 hours before serving, start boiling water. We boiled about 40-50 quarts of water per cooler.
Split the cobs evenly between coolers.
Pour boiling water into coolers with corn.
Close lid and don't open for at least 30 minutes, or until time to serve.
-Corn takes about 30 minutes to cook. Will stay warm in cooler for up to three hours, unless the lid is opened :)
-Don't worry, the corn will not over cook.
-We assigned a couple of people to sit on chairs and serve the corn with tongs. We had the servers open the small "door" on the lid of the cooler instead of the large lid; this allowed the water to stay warm until everyone was served. Place a bowl of melted butter with brushes on a table for those who want butter.
-You may use any amount of corn, follow directions above. Don't fill the cooler more than 3/4 with corn to allow for an adequate amount of hot water to cook the corn.
-We used most of the corn we cooked, the extra cobs were cut up and used in a Southwest Salad the next evening.