I always think it's a good idea to actually update these "question" threads.

I continued the external in/out with rigid plastic Domus pipe with the clip around insulation. For everything I could get to I've spray foamed gaps and taped all the joints. Final link was with a rubber joiner which of course left 100mm or so uninsulated so I repurposed some of the flexible pipe insulation to wrap around that and ensured it was all well taped.

On the supply feed from the unit to the house I added a 300mm metal attenuator and tried doing the connection to the manifold in semi-rigid aluminium. It was noticeably noisier than before and you could feel the vibration/turbulence when you touched the outside of it. Replaced yesterday with more rigid plastic pipe and its super quiet again (used the rubber joiners at both ends of this pipe as well.

Will have to wait until next year to see if I still get any condensation....