Tee Shirt Quilts

Four years ago I made a tee shirt quilt for my grandson for his high school graduation. It was a joy to make, he loved it and it was a real conversation piece at his graduation party. Now a granddaughter will be graduating in May and would like to have a tee shirt quilt made for her, too. I know the assembly layout but cannot remember how to stabilize the tee shirts. I cannot remember whether I used a fusible interfacing or whether I fused the tee shirts to muslin pieces. Can anyone help me so that I can have this ready for her when she graduates? Thank you in advance for your help. Judy