If you want to have an easier configuration, you can use worldquote module that you will find in the contributions directory.

I used it before coming back to the core flatrate and workflow-ng and it works pretty well, but as Ubercart is growing very quickly and, I a lot of major changes since the first beta bring a lot of problems for contributors that don't always have the time to adapt their code (like me). That's why I returned to core to be sure my quotes will keep compatible with the last releases of Ubercart.

And the flatrate/workflow system is a lot more powerfull than using worldquote. It's just OMG longer to configure

I profit to my answer to post a very little suggestion, don't know if it depend on ubercart of worldquote, but it would be really good to have a between rules in the worldquote weight package condition. It would allow to set it up in only one condition (between 1kg and 2kg for example) instead of definind 2 rules (1 : > 1kg 2 : <= 2kg).