I took the suggestion from many threads and converted an Igloo Ice Cube cooler to a fermentation chamber. I took off the lid and replaced it with a lid that I made out of insulation sheeting. I cut a whole in the insulation sheeting lid to allow the neck and airlock can poke through.
There's a picture of one somewhere in the old threads, maybe from Yooper.
I'm lucky because I use a Better Bottle carboy for fermenting. The 6-gallon Better Bottle is short enough that the sheeting lid can get low enough that it fits as well as the regular lid, i.e. there's no gap for air to get into the cooler. Actually, I taped on a second layer of sheeting so that the lid hugs the inside of the cooler as well.
Regardless, the cooler works really well for maintaining the air temperature surrounding the carboy. But remember, it's the temperature of the wort that counts, not the ambient temperature. Again, using someone else's suggestion, I took some bubble wrap insulation (actually, I ripped in two a bubble-wrap envelope and used that) and taped it to the side of my carboy. Then, I slide my temperature prob in between the insulation and the carboy. This gives you a very close approximation to the wort temp. My temp probe is wireless, so I can check the wort temp from my home office.
So, I stick the carboy into the cooler with the temp probe, and then add a couple of frozen water bottles. I adjust the number of the bottles to get to the correct temp. I don't use water in the cooler because my Better Bottle has a spigot and I don't want to have standing water sitting in the spigot for several days. But water would be more effective. Anyway, I have to change out the frozen water bottles twice a day for the first three or four days. Then once a day for the next three or four day. Finally I let the carboy come up to room temp for the remaining couple of week. But, then again, I'm lucky enough to have a basement that's ~68 degrees all year round. But even if you didn't, I'd be that you'd only need to put a single frozen water bottle into the cooler every day or two to maintain 68 degrees.
So the cooler method works pretty well. Someday I'll convert a wine cooler or fridge, but for now, this is fine. And, again, I don't add water to the cooler; I just cool the air. I'd suspect that water would work better and mean that you'd have to change out the frozen bottle once a day instead of twice a day during the early days of fermentation when the wort is producing a fair amount of its own heat. After those first couple of days, it really doesn't take much to maintain the temp inside the cooler because the wort isn't producing any heat.
Hope that helps.
