Here's how I baste:
http://www.quiltingboard.com/tutoria...mq-t91013.html I've done queen/king size quilts over 10 feet wide using this method and spray basting (I quickly tired of doing all that stitching by hand). So far I haven't had one single wrinkle in my backing, and I'm FMQ without a long arm so my basted quilts get handled a LOT as I'm quilting them! For the really wide quilts I use 12 foot boards and 3 four foot tables pushed together end to end so it all lays flat as I'm spray basting.
I always starch and press both the backing and the quilt top before basting.