Prism99

I don't get puckers. The tip I have to offer is to *heavily* starch the backing fabric before you layer. This stabilizes the backing so that it is less likely to get stretched or distorted while you are machine quilting. Some machines are worse than others about this, and your machine may be one of the bigger offenders.

Anyway, here is how I starch. (I starch the yardage before even sewing the backing pieces together. You could also starch the backing after it is sewn.) I mix a 1:1 solution of Sta-Flo liquid laundry starch and water, then use a large wall painting brush to saturate the yardage. My kitchen island is the right height for this and easy to clean up afterwards. I wait a couple of minutes to allow the starch to be absorbed by the fabric, then toss in the dryer. I iron with steam.

This is the heaviest amount of starching I have been able to achieve. It has not interfered with spray basting. I never stretch the backing; I just smooth it out and, on larger quilts, secure with clamps to keep it from moving around.

If you have an already-layered quilt, it still helps to spray starch the backing (and the top can benefit from this also). For this you would want to lay out the sandwich on a large flat sheet to catch overspray. Spray the starch on from edges towards center to minimize overspray, and let dry. A fan speeds the drying process. Spray several layers of starch this way. Toss the sheet in with the rest of the laundry.

Starch stabilizes fabric so it does not stretch or distort while you are working with it. The other techniques mentioned help too, but starch (in my opinion) is the key.

Edit: Also, are you using a walking foot when you SID? That can be an important factor on some machines for keeping the top and bottom layers together when sewing.