The tube quilt back method is one I learned a long time ago at a quilt class. I have the printed hand out but have not seen it anywhere online. Maybe someone here knows about it and if it is available. There is a youtube video but it's rushed and she tears the fabric. Same results just a different method.
https://www.youtube.com/watch?v=0WJt...avenlyStitches
The way I was taught was to use yardage twice the length of the quilt top. Add 1/2 yard to the total . Open the fabric and fold in half (if using two different fabric cut each the same length) Cut into two equal length pieces. Sew the two pieces together right sides together. Now you have a tube. Fod the tube in half longways seam to seam. Crease the fold .Unfold. Cut along the fold (video shows tearing it) Only cut the top layer not the bottom. Now you have pieced backing with no middle seam.
In class we each made a mini backing from a rectangle scrap of fabric. This assured us we wouldn't be making a mess from a lot of fabric. LOL
I made a quick mini from a scrap so it's not proportional but shows the steps.
.