I added the Caterham insulating sheets, adapted to fit my older 7. I wrapped the exhaust with tape. Both seemed to help a little. I also fitted a cutoff to the heater matrix (which some modern Caterhams have as standard), my thinking being to prevent a large heater full of hot water sitting above my legs. Best mod I’ve seen, and I will do one day, was to fit a pipe to the footwell with a sink plug operated by foot to get air flowing down there.