Linear Rail Slab Flattening Jig Anti-Racking Device

I am in the process of making a slab flattening jig with linear rails.
In the process I realize that the jig can rack a bit when moving. This was my idea to fix that issue.
Ive seen others add a piece of plywood in between etc, but this makes it easier to break down and store it when not in use.

Please remember THIS IS FREE... Also, this is a work in progress. It may not work 100% on everyones rails.

Thanks

PS use 20% infill roughly, but make sure to use at least 4 of each, walls top and bottom