I agree with Acid... you'll need to get a cathode inside that tank if you want any action. Unfortunately, the cathode area will probably be quite small compared to the internal area to be anodized.
And you'll need to circulate acid through the tank to get rid of the heat that's generated inside it and to get rid of bubbles that form. Maybe a piece of aluminum tubing that's got holes in it that you can shove into the opening.. Pump acid through it so it shoots out the holes and gives good circulation and turbulence inside the tank?
Have you done a square footage calculation on it yet?
A 2 gallon (462cu in) tank that's a perfect sphere would have a diameter of roughly 9.6" and an internal area of about 190sq in. (2sq ft).
A perfect cube would be about 7.75" square and have an internal area of about 360 sq in. (2.5 sq ft)
Odd shapes get tougher to calculate.
I hope you get the job... I'm curious how it goes and what solutions you come up with to make it work. Sounds interesting.
steve