I have a fuel cell on my pillon, but it's a little bigger than what you describe - just over 4 gallons. It was actually made for a K1200LT to bring it exactly to the IBA limit of 11.5 gallons, but I was able to buy it from someone (with a K1200LT!) who decided to go a different route.
It's mounted on a Jesse plate and is quite secure.
is the manufacturer of my cell. There are others.
Make sure you ground and vent your cell. Drilling into the flange on the side of the fuel cell is a little scary, but take your time and it'll be okay!
I have a quick disconnect on the line from the cell to the flange so I can just disconnect the QD and take off the Jesse plate and it's off.
Also, you might be interested in a custom fuel cell cover by Linda T. I have one on my fuel cell with a couple pouches on it and I LOVE it. http://www.customtankbags.com/
might be the company someone else mentioned. I love this one because it looks like a little keg!