The fixed position seats really need attaching to the car at a minimum of six points; two through the front lip that sits on the floor, two more in the bowl of the seat, (under the cushions for your bum), also through the floor. Then one either side of the seat back, with the supplied aluminium brackets, to fix it to the rear bulkhead.
Even then, because none easily fall on existing steel work*, as a bare minimum, you need large spreader washers. Ideally, you would weld in steel straps or box section anchorages.
*unless of course it's a car with the lowered steel floor pans.
If it was purely for road use with a lightweight driver, you could probably get away with just the front edge and the rear brackets being fixed. But be warned, under serious cornering loads, they flex and move.
Personally, I wouldn't have the fixed position JK's again, for the lack of strength and stiffness the single skin construction causes.