I've used basting spray on large projects by centering and then clamping the batting down to a table. I do not stretch or pull on it.
Spray one end and settle the backing in place, smooth out any wrinkles. Clamp this down.
Lift away the backing from another section of the un-sprayed batting. Spray this section, settle backing in place, smooth and clamp.
Repeat until you've covered the table surface with sprayed layers.
Un-clamp and reposition the batting as before. Repeat the process as you spray and baste the whole quilt.
Jan in VA