I bought a big sheet of insulating foam board (very lightweight). I put this on two (lightweight) plastic sawhorses. Then lay the back (print side down facing the foam board, then I roll the batting and as I lay it on the wrong side of the backing fabric I spray and smooth the backing to the batting. Then do the pieced top the same way (spraying and rolling a small amount at a time). Has worked great for me and the sawhorses will fold away easily.
Also, the quilt nor the batting ever slips so no need to pin at all and all the spray washes out once everything is done. Love it.
Hope this helps. I totally understand as my knees are shot and I can't crawl around on them either.