Have to agree with using a cooler as your reservoir. I have used the tubs from Walmart and they work. The problem is, after a few months under the lights they tend to weaken and bow. This is alarming when you consider there is 20 gallons of "water" in there. The way around the issue is to use two tubs (one inside the other) to add structural integrity to it. When I built my ebb and flow system, a cooler made perfect sense for the reservoir. Would not use anything else at this point.
Used bubble buckets as an experiment once. They work very well, but definitely more "invasive" with all the lines required.