I also use spray adhesive. Usually the kind made for fabrics is considered safest, but meh. I've always liked krylon but the others are okay too. Don't use repositionable spray as that doesn't hold well. In my experience 505 is more expensive but not any better than krylon.
However, you need a smooth surface to spray baste (at least the way that works the best for me). I lay the backing out and tape it to the floor so it is tight and then add the adhesive-batting-adhesive-top, unfolding the other two layers so they are centred on the backing. That way you don't have wrinkles and you can true the top with the backing. You do need to lay newspaper or similar down on the floor beside the backing to keep the adhesive from covering the floor. And it requires a deft hand--even the best adhesive can be applied too liberally or too lightly. It takes some experience to get just the right amount to hold the quilt together well without causing gumming, clogging or stiffness. I also always wash the quilt after I am finished in hot water with synthrapol, which will take most of the adhesive out nicely.