As it happenes, I spent the afternoon fitting a version of the X-Eng Kit to my discovery. The circiut is simple and robust. I made my own cables up, since the standard cables are meant for batteries sitting next to each other (like in a defender battery box), but Simon will do custom lengths if you need them.
Sorry if this dosn't help much give a wide view of the market, but I am happy with the setup!
Cheers
Mark