My courier has a list of prohibited items, firearms, chemicals etc. among them was animal remains. I don't consider the skins as remains so just said they were sheepskin rugs to be on the safe side. I packaged them very well in several layers of plastic bags and a strong box, also covered in plastic, so can't see that there would be any issues.
I salted the skins in the stable, which only stores old gardening equipment and bits and pieces. There is no running water directly in the stable but there is a tap not far away. Why would I need running water?
OH collected the skins from the abattoir and he took a big plastic box with a lid to put them in.