[SteveB]

There are three ,maybe more, approaches to seats in a car each will present different methods that should be OK from an SVA or safety point of view.

First if the seat frame is in fact part of the chassis construction it is integral and may only need a simple formed pad to be securley fitted. Original type mono's / Superformance etc are this way. ( no seat position adjustment)

Second a seat shell can be fixed through the back, sides and base; this can be onto a relatively thin floor sheet as ther are other strong back and side fixings. Also non adjustable.

Third, if you need to have adjustment and or access to the small storage space available behind the seat there will need to be a runner system and lockdown feature, if it can tilt forward. This would be unsuited to fix to a thin ali floor sheet; seat mounting bars would be needed.
As I recall these were on my previous KVA build and also on the GTD and others. My MDA build has them now sandwiched between the inner ali floor and the stainless undersheet. Picture of the frame before painting etc attached.

There are probably more methods

Regards

Steve