Merv you are right, it's required by ADR 82/00 that you have an immobiliser. And I know for a fact that your engineer will check you have it.
A 3 point unit is the go.
I supply the Rhino JAG unit for RCR cars. Great value and they are reliable. John has a Rhino in the Cobra he races and environment wise it doesn't get much harsher than that.
http://www.rhino.com.au/?p=product_info&id=1589