There are two things I do to prevent puckers.
First, I heavily starch the backing fabric before layering, using a 1:1 solution of Sta-Flo liquid laundry starch and water. I "paint" this on with a large wall painting brush until the fabric is saturated, toss in dryer, then iron with steam. This stiffens the backing fabric so it is unlikely to stretch or distort, and makes it difficult for the fabric to fold over itself.
The other thing I do is spray baste with 505. This provides an all-over connection for the three layers unlike, say, pins at every 4". This continuous "glue" prevents the layers from shifting.