The storeitcold site has all kinds of plans and ideas. Mount the a/c high to cool up top and let the cold air settle to the floor.
They recommend R25 for the walls. Pink insulation board is R-5 per inch. I used 2 layers of 2" and 1 layer of 1", offsetting the seams. My cooler is 8x8. I didn't use a floor drain but rather sloped the floor to the door so I can sweep water out.
A cooler will serve as a warm room in the winter as well as being a cooler the other 3 seasons. I put a small space heater in it to keep it about 40 to 45 in the winter. I store stuff like canned fruit, pesticides, and paint in there during the winter. Watermelons and cantaloupe will keep for a month or more at that temp. We ate the last watermelons in mid-Oct. this year.
