[JasonCC]

I purchased this pre covid. Then I got a flat pack and no rez. A friend of mine assembled these for me. The first question is whether the crossover should be at the top of the tower. Second, he lined the cabinets with no rez but did not use any polyfill. If I add some after the build, how much weight of polyfill for each speaker?

[Hobbsmeerkat]

For ease of access I would mount the crossover to the back wall, just below the woofer.
As far as polyfill, a loose 2-3 inch layer along the back wall will be plenty.
So long as it doesn't block the port you're in good shape.

[JasonCC]

These have been converted to the  X-SLS Tower version. I have 2 1-pound bags of polyfill from parts express.

[JasonCC]

Bump:

Since these are now the tower version, is there any advice?

[corndog71]

I don’t think you need even a pound of polyfill.  Put a handful behind the tweeter and woofer and leave a hole for airflow down the cabinet. 

[EdwardT]

Bump:

Since these are now the tower version, is there any advice?

I put the crossover on the back wall behind the tweeter and that was very convenient. Your arm will fit inside the cabinet to allow fishing the input wires out to the connectors so you can plan your wire length, too. After that every assembly action is really easy and you end up with a superior sounding speaker.