DIMS weight rate estimates

Hello,
We ship large, lightweight packages of variable size, and our shipping rates are largely determined by the size of the package(s). ShipStation is integrated as a Shipping Service.

I would like to see an option in the set-up to add multiple default package sizes, and in the "Get Shipping Rates" pop-up to to be able to select which package size / # of packages is sent to ShipStation for a rate estimate. This would greatly increase the accuracy of the shipping rates and make this feature functional for us. 

If possible, just having the shipping rate estimates calculated after the package details are entered in the Pack Step would be acceptable.