Need to ship combined different weights world wide

Hello,

I'm trying to work out how to ship 12" 10" & 7" vinyl records as combined weights but it depends on what the buyers choose, i have already set up "Weight Based Shipping" "Royal Mail" and "Parcelforce 48" for 12" vinyl records which work fine on check out but just can't work out how to set up shipping for 10" and 7" vinyl records, i have tried searching for info on how to do it without messing up what is already working fine. would be grateful if someone could point me in the right direction as to how to go about this.

Thanks in advance.
Paul.

If you can describe your shipping rates in a little more detail, we might be able to suggest something. If you're just looking for weight-based shipping with more options, I have this extension: Weight-Based Shipping