Decided to have a go at back opening on a tutu I started today. I decided to try to do a bit of a fusion so I extended the back pieces by 1.5" as in non-stretch and stitched a centre back line in both back pieces for my fold-back placings. I intend to turn under the right hand side and place hooks underneath, quarter inch to the right of the c.back edge. I will leave the left hand side extension as the underlap, stitching the eyes level with the centre back marking. Just as you would with a non-stretch. As HD says, with fabric and lining layers it seems stable enough not to gap between the hooks/eyes.
I decided to open the skirt a bit too to help with pleated net stretching over the seat area, so I put a seam in the back of the pants and added an extension of again 1.5 inches to the back edges but only to about 3" down. Up to now I have only pinned the bodice to the pants but it looks like it is going to work okay. By the way, I am using the Jalie tutu pattern (with my own amendments!). Quite pleased with myself today
Will let you know how it goes. Ann x