I used a large chest freezer (minus the top) way back when I was catching my own bream for jug fishing for catfish. Water stayed cool enough to keep the bream alive as long as I wanted to fish, but I was through fishing jugs before summertime got here. But you bring up a very interesting question and I think a working freezer set up on a timer would be the ticket, especially for minnows. I dont know if you'd want your water COLD because once the minnows hits the lake water they'll curl right up on you, but COOL would definitely keep 'em alive during the summer months and fairly easy to aclimate 'em to warmer temps (in the minnow bucket) before you started fishing with 'em. That's a great idea. Thanks. I might start looking for a good used one myself to replace my 2-55 gallon barrels I currently use.:p
Health nuts are going to feel stupid someday, lying in hospitals dying of nothing.