I’ve been rethinking the sub-frame assembly. Originally I had planned on notching the longitudinal and latitudinal extrusions together, but this may have compromised the strength of both.

Lapping them together with L-shaped extrusions top and bottom may be a better solution. This allows the longitudinal and latitudinal assemblies to float independently of one anther until final assembly – allowing me to pick-up any tolerance build-ups I may encounter.