Actually your bike looks cool without the side panels, and I noticed the space where the radiator and puke tank would go behind the gas tank, so watercooling is a possibility.
As for the Rubbermaid, here's a link
You want the 8 gallon, it fits perfect between the passenger hand grips on the frame.
Also consider a bungee net, I bought the largest one I could find, and it holds all my gear on the back of the Big Ruckus fine. Here's a pic of my BR with the Rubbermaid on the back and the net holding it....