Adding a big, long zipper to an existing pack

I haven’t converted a top loader to a panel loader but….

Questions:

Does your pack have any kind of frame or a padded back panel?  (makes the project harder and calls for a different method)

Are you wanting to sew the existing top opening shut?  If yes, then that opens up (pun not intended) possibilities.

Do you want opposing zipper pulls?

Are you wanting a waterproof zipper?

Zippers are hard to sew on a curve because the stitch lines are on different radii.  Waterproof zippers are harder yet.  For instance, if the center line (cut line) of your ‘U’ follows a 9″ diameter, and your zipper stitch lines are 1/4″ from that, then the inboard zipper half stitch line follows an arc length of 13.35″ and the outboard zipper half stitch line follows an arc length of 14.92″.  My apologies if you are already familiar with this problem.

-Lance