My Litchfield Type 20 hatchback has no carpet / floor cover in the boot. These were JDM sti’s converted to T20. The cars were imported by prodrive, it was delivered new without this trim, presumably because many were intended for motorsport but I’d like to install one, but I do have a full size spare which sits higher than floor. Has anyone else done something to resolve this? I don’t think I can go space saver, due to big brakes.

 

Cars with the carpet also have a floor made of hardboard so as to support the carpet across the wheel and since the carpet is VERY thin, across boot floor ridges.
With a full size spare I'd suggest building the boot floor up using polystyrene insulation cut to size and sealed with gaffer tape or parcel tape.
If you then use a hardboard floor too, the insulation can have voids in it for storage, warning triangle etc etc.
Just my take.