Guys,
in the end I decided to go the "traditional" approach and used closed cell foam under the leather.
This gives good firm support for this " high stress " area and is resistant to moisture.
The pic shows the old leather removed and demonstrates just what a harsh environment that is down there at the junction of the chassis and floor!
The leather had obviously become wet and then dried, ( probably on more than one occasion ), shrinking as it did so, pulling away from the floor where it had been tacked down. ( straight horizontal line denotes chassis/floor line angle )
The worst area is just forward of the chassis cross member (probably related to water ingress down the leading edge of the door). The leather here was as fragile as parchment!
As always, thanks for all suggestions.
Neil.
You need a bit of this 