I just did an almost full-size D9P variation and was going to back it with some fleece that had a pattern so I could keep an eye on any possible stretching.
Despite a good basting, careful SID quilting, etc., by the time I got to the last two rows, the pattern was still lining up (front to back), but the fleece itself had stretched badly (and not from lack of watching to prevent just that).
It killed the quilt and while I may try it for a baby quilt, I definitely will not ever do this again. Besides, it was inordinately heavy. Very warm, but quite heavy.
I had also had it on a full size table during quilting, so none of it had hung down to stretch it out. I'm actually not sure what happened except that it just gave way to its inherent stretch.
Live and learn life's lessons in humility.
P.S. The cat and the dog both love the fleece side, stretch notwithstanding.