I have not started my shirt yet but I googled Tee shirt quilt and you get a lot of info there. And yes you should use a very light weight fusible interfacing.
I was mostly wondering if people quilted stitched in the ditch. The ones I have seen on here look so nice I like the off centeerd rows but I don't know how to achieve that look. I am someone that needs a pattern or doesn't trust my own idea. I hate when that happens.LOL
Pickle