I agree with Pewa88. I have not had much variance between before and after quilting even with a densely quilted quilt. maybe 1/2" but in my experience that has been both side to side and top to bottom and my measurement is usually the same no matter where on the quilt I measure. I can fix any small variances by blocking. If my quilt is nice and square going on, it is nice and square coming off. You say it is drawing up in the center only? So when you measure the length of the completed quilt you are getting a variance of 3/4 to 2" in the center part only?? For example you measure the side from top to bottom and it measures 90" then you measure the opposite side and it is also 90" but when you measure the center from top to bottom you are getting a different measurement?
You also have me confused with this statement: "When you get 4 poles all pulling the fabric different it does nasty things to the quilt! "
4 poles?? Even with a deadbar and loading the top (as opposed to floating the top) there are only two bars that are affecting the tension on the quilt, the take up roller and the roller your backing is rolled up on. The deadbar is not playing a role in it and neither is the roller that your top is on (assuming you did not float the top).
I have a 10 foot rack and my poles were delivered in a mini van, pretty much the way you described. But the poles are made out of powder coated steel and that would definitely not warp them in anyway.