I've had oniony/cat piss before. But otherwise have had really good luck. Never plastic tho. Will find out shortly how it went this year as I'm kegging an IPA tonight done with a LOT of my homegrown cascades. See link as I'll try to keep it updated with how it goes. Homegrown Fresh Wet Cascade...
Just to help a little - the swamp cooler part is draping a towel or shirt or something in the water and up over your fermenter so that the water wicks up the towel/shirt and evaporates and cools the wort.
Just brainstorming here: If you are really worried about temperature getting out of...