Hi,
I'm making a start on Backpack #3. Currently collecting all the various bits. I couldn't find any suitable exhausts so decided to have a ago at making a 3D model. I have printed this (in resin) and I was super pleased with the final result! You will need a jubilee clip/worm drive hose clamp to finish it off, the hose is optional as I have included one in the model. A bit of light sanding might (probably will) be required. Let me know what you think!
https://www.thingiverse.com/thing:5461254