I spray baste outside (read the warning label on the can!). Try to choose a time/day when it's not too breezy, I put my backing on a bed sheet bigger than my quilt backing, taped to the patio if necessary, batting over that, quilt top on top, spraying in between layers as desired. I use blue painter's tape to hold everything down if necessary if there's a breeze. Then I transfer the sprayed quilt to my table inside the house and smooth and reposition as needed. I throw the sheet in the washer and all done.