A 3 ton Field Kitchen fits on a support vehicle to the tune of 1 slot, and support vehicles are notably and explicitly in the rules text space-inefficient things. Same goes for MASH units. LB-20Xs can be pod-mounted, and they take 11 crits at a time. Hell, an Arrow IV can be pod-mounted. They can be crewed by support staff and other infantry.
That restriction continues to make no sense.