How much cribbing is enough?

We are currently in the process of writing specs for a new service/hazmat/rescue truck. I already know there is not a truck big enough to do all three. But we have to do hte best with what is available. Our current truck is too small and quite overloaded so how much we carry of something has always been based more on space available then on the need for it ( as the needs normally outweigh the space). We currently have a set of air lifting bags and assist the local rescue squads with auto extrication. We carry enough cribbing for a standard 1-3 car MVA but it is limited. We are looking at a medium duty type rescue truck and need to allow space for the other functions of the department. I have seen lists that show the reccommended amounts of cribbing a heavy rescue should carry; does a list like this exist for a medium rescue? What is reccommended?