I don't think there should be any trimming to do unless mixing T-Loc and Classic Systainers and inserts.
Seth
From what has been posted here and looking at some pictures, I expect to clearance the universal tray for vertical ribs that are in the Systainer II because I want the tray to sit on the bottom.
I ordered both the tool tray and the universal tray for the T-Loc Systainer from Lee Valley. A secondary benefit is that I could use the tool tray, which is advertised for the Systainer II, as a template to trim the universal tray. Buying both is still less money than the Tanos dividers from Woodcraft.