For those of you that don't know, I just figured this out today, if you haven't figured out how to do supply lines yet, look here. When you are in the workshop,go find a settler. there will be a button prompt, LB, and you can make that person into a supply line between that town and which ever you are allied with. You can also press X to move a settler from one town to another. Doing this will connect your workshops together making building among multiple bases way easier. Hope this helps. Sure helped me