Hey Patrick, a 12v Gell Cell like this one [link=http://www.sloughrc.com/asp/default.asp?itemid=O-NP7/12]HERE[/link] should fit in your box...you should be happy with a one motor box...the only trouble is when your running in a high compression motor they can struggle a little...easier to pre heat engine.
I also bit the bullet and recently bought a starter box and are really happy with it...beats the heck out of pullstarting...oh and speaking of engines I drove my friends XUT Truggy the other day with a 5 port Go-Tech .21 and boy was I impressed, great power and when my K4.6 (which I have in my XUT) was out of fuel he still had 1/4 of a tank...and his was quicker...