First time poster, long time lurker. I've been working on some inserts for the new systainer3 M line, and figured others could benefit from my SVG files. These are based on an M112 (haven't checked it yet against the taller M line systainers, but I do plan on working my through the rest if there are differences, which I'm sure there are since there were with the T-Locs). I Modified [member=41832]WastedP[/member] 's L lid to fit the M width as well (hope you don't mind).
Layer 0 - base layer with molded X shape cut out
Layer 1 - between layer 0 and 24mm up
Layer 2 - from 24mm to top layer
Layer 3 - top layer with cutouts for lid protrusions.
Lid - Lid
*edited: Layer 0 and Layer 1 were tight fits and needed to be slid in at an angle under the lid side hinges, which can be problematic if you're doing thick inserts, so I made alternate versions that have enough clearance around the hinges to drop straight in. Also attached zip file instead of individual links.