Christina, tubes are definitely tricky. Honestly, I don't know anyone who uses tubes and CS.
Right now, with the limitations of fractions under 1 inch, it is a real problem for your items.
My best advice to you would be to contact support directly and ask them if they have a suggestion.
Put something like Calculated Shipping Problem as the subject line.
Etsy Support
https://www.etsy.com/help/contact