While there is not currently a Tube package type available in ShipStation, Stamps.com recommends using the package type Package for these shipments and entering the appropriate tube dimensions to ensure labels are charged the proper rate.
This is true whether you are using your own custom packaging or the USPS provided Dual-Use Priority and Priority Mail Express tubes.
This article includes additional information specific to shipping First Class and Priority via USPS using tubes. For each service, the same weight and size restrictions that apply to packages also apply to tubes.
USPS First Class Mail
Max weight: 15.99oz
Max dimensions: (L) 22" x (H) 18" x (W) 15"
For tubes, the height and width will be the same.
The rate is determined by the weight of the package.
USPS Priority Mail
Max weight: 70lbs
Max dimensions: Length + Girth < 108"
Check out the USPS guide to help determine the girth of your package.
Priority Mail is zone-based pricing. That means for certain zip codes you will have to enter the dimensions of your tube in order to obtain the correct rate. Entering dimensions is always recommended to ensure your packages receive the correct rate from the postage provider. Incorrect dimensions can result in packages being returned, or rate adjustments applied to your postage provider account after shipping.
USPS Dual-Use Tubes
If you ship using the small or medium Priority Mail or Express tubes provided by the post office, you will still select package type Package and enter the dimensions for the tubes into ShipStation.
If you use a specific size of tube regularly, create a custom package type in Settings > Shipping > Packages. It will then be available as an option in the Package drop-down menu for your orders and will auto-populate the package dimensions.