ATV Rack Cases

I was in town the other day and saw a bunch of carry rack cases in Wal Mart for ATVs, I did not have the time to stop then, but want to get a chance to look at them when we go back in a couple of days. See if I can get some ideas for how to attach the one I want to build to the rack on my ATV. Right now I am thinking a couple of U bolts to go from underneath up into the case, but I would like to have it be able to be removed with relative ease when I want the thing off the machine, so I am still considering ways to attach it.