when i installed the new carpet in my 69 charger this spring, i put the foam square between the carpet and foam, correct or not.
my thinking was the foam would act as a moisture "deterrent", keeping any moisture away from the carpet.
however, i installed a "gasket" cut from a roll of gasket material the shape of the foam gasket, [slightly larger in fact] sealed to the floor with a thin smear of seam sealer, before the foam square, just to be absolutely sure no moisture would come through this area. i know this isn't correct by any stretch of the imagination, but that's what i did anyway.
i also greased up the gas pedal studs with high temp copper anti-seize before i nailed down the pedal for the final time. i will more than likely never remove the pedal in the rest of my lifetime, but did so "just because".