There's a new option available now - I've been testing it in a few cars and it's a direct solder-on replacement for the stock FETs just like the IRF7389s are but with a much lower resistance.
Becuase they switch at voltages very simialr to those found ont he XMod and Mini-Z circuits they operate at their peak efficiency
w00t!
Check out
www.ausmicro.com Mini-Z and Xmods forum for more details - Once it's all sorted 'there' I'll repost it here.
A.