I thought about what everyone was saying about the quilted seat coming apart at the seams and a light bulb came on. What if you use a sturdy, like a cotton twill for the base, and applique (by machine) the blocks to the solid piece of material? Then layer with batting and put a sturdy fabric on the bottom. It would make a 4 layer quilt, but would be sturdy and sitting on it should not have any impact. You could make the top using the twill as a base for a Friendship braid.
http://100billionstars.com/2013/06/f...quilt-pattern/
You could make any normal block, and sew them into rows, then use a QAYG to layer the blocks onto the twill. When you finish the quilting, you would have many more seams to keep the 4 parts together. The twill would add as a foundation.
Edited to add: I love that idea of a foundation fabric....I may use it myself for a chair cover I have been thinking about making.