[MrBasse]

The protrusion of the bearings on the kit frame would require a slot of slightly less than 1 ply on standard 3/4" plywood. If that puts the bumpers tight against the frame it would be stronger than leaving an unsupported 1/8 gap for the remainder of the frame. Do you want the bumpers to be supported by the frame, or by 12 bolt heads and a bearing? Leaving the bumpers supported by such a small surface area will place all of the force onto your mounts and is more likely to compromise a less than "robust" attachment design. In my mind this presents a safety hazard. To me, Slots are the way to go, but FIRST and FRC inspectors have some rules that only make sense in FRC, not necessarily the real world. Even then some of them don't make sense in FRC...

In short, keep slots shallow and blind and make sure your mounting points take all of the forces straight to the frame.