My first string quilt I used a muslin foundation. I hand quilt and the extra layer made the quilting tedious so the next couple I made I sewed the strips together and had my plastic square close at hand to make sure I had the pieces long enough then I spray starched them and squared them up, it worked fine and made it so much easier to quilt through. I don't think you need a base unless the fabric is really wonky.Here's an example