Years ago, I pinned quilts on our carpeted floor. There was enough space and I could pin the backing to the carpet first. But we no longer have carpeting, and it's difficult to get down to the floor now.
Then I pinned quilts on our king size bed. The best place, though, was the community room at the library, where we could push three tables together.
Then I tried the spray basting. The first quilt I spray basted was on our kitchen counter/bar. The overspray went everywhere, the counter, the floor, everything was sticky. It took at least 6 months to clean it up. The second quilt I spray basted, I did on our deck. I figured overspray would be less of a problem outside, but I still had to get down on the deck. The third one I did on tables pushed together. That worked best.