Hmm concrete. Sounds like it would work. I have a friend who wont buy a chiller and got sick of using 2 lt's. He did almost the exact thing your thinking.
He took a large rubber maid, cut the correct holes for his 1/2" barbs and such. He lined the bottom of the rubbermaid w/ insulation. Then he set the normal controller/res (witch was the same rubbermaid just smaller) and hooked up all the tubing. Then he used Great Stuff foam insulation around the cracks between the larger rubbermaid and the controller. He also lined the larger rubber maids lid w/ insulation. It brought his temps DOWN. He didnt give me numbers he just said it worked great. I also had him build a box for his airpumps w/ 4" ducting blowing in cool AC air.

I started thinking a little after this and you could use a larger cooler to place your res in as well. Or just use the cooler as a res. They would all help w/ temps.
I also think concrete would bust most rubber maids but I could be wrong
The White Snoop Reviewed by The White Snoop on . Creative thinking (Reservoir) Ok with summer coming up reservoir temps will be a problem. I could run a chiller but donā??t really want to pay for it or the elec that comes with it. Ice in 2 liters works but I think the water gets to hot and melts it before it really it really has a chance to work. So all this got me thinking What if you were to take one small tub and put it in a big tub and pour concrete around it. this would provide it with a in the ground type cooling. The concrete wont heat up as fast so it will stay Rating: 5