I’m sure what I’ve done here is a big no-no. I just notched one side of the provided fan duct fitting (as in cut out the round cylinder wall from an entire 90 degree section minimum) and slapped this little filter box on it, which is packed with charcoal filter bags I can swap out.
I still smell a little bit of burnt wood while lasering but not too much. I can feel good airflow with my hand at the vents in my filter box. Anyway, I’m sure a similar solution would let you adapt to a rectangular profile. As others have said you might want a supplemental fan at the far end to help with air draw since you will be constricting flow right ‘at’ the fan.
Even in my pic with only the part of the fitting that was intended to slip into the hose notched it’s obvious there’s still a good inch or so of depth to the enclosure outer face. I’m sure you could design your own 3D printable total replacement that would smoothly direct the flow 90 deg with a lower profile than the hose diameter and save a little room without too much constriction.