Yes agreed, the weight is what it is. In my case, the Irwin bag had a chamber at the base that was accessible from both ends of the bag - in theory for holding a cordless drill or something - but when the bag was loaded up, over time this chamber collapsed, making it useless! Obviously the veto doesn't have this feature/issue, so not a problem.
Anyway, this is my quick n' dirty insert, made from scraps of 12 and 9mm ply...
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in situ, all my commonly-needed tools at the top so no need to take it out of the Sys 4
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and broken down into its components. Each tray has a slot cut into the base to stack over the handle, and each holds something 'broadly specific' i.e. it's not an organiser where every tool has its place, but all the electrical/testing tools, fuses, earth sleeve, etc.. are in one tray, all the heavier-duty pry-bars, vice-grips etc.. in another.
That's the theory, anyway - I'll see how it works out in use over the next few days
Cheers, Pete