We cut off the original Amel ducting inside the cockpit locker and replaced it with Eberspächer-brand silencer (where it fit) and with heater-rated marine ducting (where Espar silencers are too long to fit or where the Amel curves are too much for the Espar silencers).
Obviously where the ducting actually goes into the locker bulkheads aft and fwd, we simply joined in with the factory flimsy-looking ducting.
We cruised the boat continuously during the 2015/2016 winter season and ran the heater hundreds of hours, all copacetic.
I guess the Amel factory ducting is actually better quality than it looks, but I am still glad the areas closest to the heater have improved ducting.
SM2K Nr. 350 (2002)
At anchor, Olbia