I don't bother to clamp or tape. I lay the back down face down, smooth the batting over it and then lay the top on. I do it that way whether I'm spray basting or pin basting. The key is to continually smooth it as you go, particularly if pin basting. For Pin Basting I periodically slip my hand under the sandwich to make sure the pins are going through all three layers.
For spray basting I lay the batting on the backing, then fold the batting back halfway, spray either batting or backing (your preference) then starting from the middle where the batting is folded back carefully lay batting back down a little at a time, smoothing as I go until I get to the edges. Repeat for other half. Then lay top on and do same thing.
Never had problems with puckers doing it this way.
Rob