If I am quilting a large quilt, I use backing for the whole quilt, and sandwich the batting for only the center 1/3 of the width. I secure that 1/3 with glue. Then I quilt, by machine, that center third.
This is the way I've found to best have it fit, and move, using my domestic machine.
Then I add the outer third of the batting, glue, and don't even hand stitch it to the center batting if I know there is enough fmq to hold it. Then I fmq that outer 1/3.
Then the other outer 1/3.
Ready for binding
I do have a 67 x 49 desk surface, with formica and I can even iron the glue without damage to the surface.