Hey Nippy, The South Africans have a saying Q How do you eat an elephant ---- A One bite at a time!
This is the approach i took,i had a general picture in my head of how i wanted it to finish up but there was too much to consider to create one big plan so basically i started with putting the tools i most use in the sytainer most appropriate for them and then worked on filling the next systainer again placing items based upon number of uses and like with with like.
In my case my LXT hammer drill and impact driver with charger and two batteries went in a no 2 with an attic lid(holding a few of the common fixings i use)i then added a sys mft holding drill bits hole saw and two quick action clamps.I enter most jobs with these in my hand and wearing my tool belt and can usually make a start without going back to the van straight away,this allows me to think through the job and then make the next trip to the van worthwhile.
I carry a Festool track saw,sander and one hand planer all the time which came in their own systainers. So anyway i now have i think 14 systainers and need two or three more but now have a clearer idea of the rack i need to build.
I spent some time on the w/end stacking them in the driveway to come up with the best stack order for me and i have sketched a unit based upon the result.
I will post some pics when i eventually get around to building it,looking forward to seeing your van when done.