I seem to remember the 'Icing Let Down' was 6000 RPM, all the way down until sure of landing. 6000 was to be set before entering cloud during the let down. Remembering to nudge the RPM up as it decayed in the descent. Then using the airbrakes/bombdoors to (try!) to control the speed after levelling off at 1500ft, then the 'gear' to initiate final approach descent. No flaps until 'sure' of landing.
Gnat = STUPRECC. I do not think ANYBODY that flew the Gnat will ever forget that!