Trace around the seat base on the back of the fabric. Cut out the fabric 3 inches larger than the traced line. Trace around the seat base on the quilt batting and cut out a pad by snipping along the trace line.
Lay the fabric on your work surface with the right side facing down. Center the padding on top of the fabric. Place the seat base on top of the padding.
Pull the center of one fabric edge onto the seat base and staple it. Pull the center of the opposite edge of the fabric onto the seat base and staple it. Do the same with the other two sides of the seat base.
Attach the fabric sides to the seat base by making a line of staples all along the edge of the fabric. Stop stapling 1/2 inch from each corner. This leaves a corner tab sticking out on each corner of the seat base.
Pull each corner tab diagonally toward the center of the seat base and secure it with a staple. Do all four corners in the same manner.
Enclose the stapled tab on the upper right corner first. Smooth the right edge of fabric at the corner so it covers the tab. Staple the edge down. Smooth the top edge of fabric, covering the tab, and staple it down. Do the same thing with the other three corners to create a tidy look.