I really like the Tailfin CargoPack but the Tailfin rack system was way too expensive.

You will need a 93mm aluminium pipe with 7.5mm outer diameter and 5mm inner diameter.

https://www.globus-baumarkt.de/p/alfer-rundrohr-aluminium-roh-blank-0763240481/

I also put shrink tube with glue inside at the ends.

At the front i put 2mm foam rubber on the pieces which are in contact with the frame.

https://www.amazon.de/dp/B0D76KTLNS?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_2&th=1

You'll also need 4x DIN 912 M5x16mm + 4 nuts for the rear end. 

The front end needs 2x 30mm and 2x 12mm M5 Bolts. 

Let me know if you have ideas for improvement.