Problem with outside is you will have temperature fluctuations. You may have daytime temps in the 50's but then temp in the 30's at night or you could have 5 days of 50's and the get a 70 degree day. Plus us you are doing outside in say a garage, just because it's 55 out today, the temp in the garage will be a lot cooler.
You are better off using a swamp cooler in a basement if you have one. Put the carboy in the cooler, add a couple inches of water, put a tshirt over the carboy so that it wicks up the water and then add frozen water bottles to try to hold temps around 50...and then just replace the frozen water bottles daily.
Member of the Metro South Homebrew League (Mash-Holes) - Weymouth, MA
Primary - Empty
Secondary - Empty
Kegged - Dortmunder Export
Bottled - California Common (2nd place, 2014 OSHC).