is this going to be a wall hanging or a bed (usable) quilt?
if it's a wallhanging it is not a problem- you can use a fusable & not wash the quilt- if it is going to be a bed/used quilt that is a whole new matter- if you plan to use batting the largest area that can go unquilted (using warm & natural or like batting) is 10"...otherwise you run the risk of the batting separating & balling up- creating areas of no batting & other areas of balls of batting.
you could use a (pre-washed) flannel or layer of fabric in place of batting- but using batting that large an area will have to be quilted if the project is ever to be laundered.