I added zippers to my Hinterberg frame leaders (that were already on the machine). It really helps if you sit down and think it through before purchasing the zippers. I found a couple of tutorials online that were helpful (will post later if I can find them again) but, even after studying the tutorials, I found some helpful tweeks for myself.
I purchased custom lengths from
http://www.zipperstop.com , which is the same company that sells them on Amazon and eBay. The first set I bought was longer than I could sew on my leaders, so the ends flopped off. Not a big deal, but I also made the mistake of trying to mark the zippers with Sharpies before sewing them on. Everything worked when I was finished, but I wanted it all to look better.
Second time around I knew better what length would work best. You cannot sew all the way to the left or right of your frame, so the length of zipper you need for the frame is that size. There's no point in getting a zipper longer than your machine can sew!
Another consideration second time around was whether I might one day have a quilt so long I would want to quilt half of it, then flip it around to quilt the other half. (So the rolled up part would fit under my longarm.) If you have a large harp, this may not affect you, but mine is a Voyager with 17" throat. IF you want to be able to do this without removing the zippers on your quilt, you want to install the zippers on the backing roller and the bottom of the top in the *opposite* direction of how you install the zipper on the takeup roller. I zip left-to-right on my takeup roller, right-to-left on my other two rollers. (Really only one of those two rollers need to be opposite, but my head starts swirling after awhile thinking about it.......) This way if I ever want to zip a quilt off to finish the bottom, I can zip it right back on.
I quilt only for myself and have not even considered taking one quilt off before finishing another, so I do not need extra sets. If you want to keep it simple, just get extra sets the same length as your original set. This way you have the choice of positioning a small quilt in the middle or to one side. Any excess zipper will hang down and not interfere with anything.
When you sew the zipper to a frame leader, you need to sew very slowly. It's not the easiest job in the world, so you may want to allow yourself some time. It's possible to make mistakes -- such as sewing the wrong side of the zipper to the leader!
Edit: One thing I have noticed after adding zippers is that it's important to use side-tensioning as you quilt. Sewing the top/backing to the zipper leaders (I did not add leaders to the zippers halves that attach to my quilt) stretches the fabric. If you do not add side tensioning as you roll, you may find that you have "ears" at the corners because the middle of the quilt is smaller than the ends.