What about measuring your zipper 1" smaller than needed and enclosing the ends with just fabric. Then when you are sewing the 1/2" side seams, you are only sewing through the fabric from the zipper and not the whole thing? Hope this makes sense. Missouri Star has a tutorial on bag making and shows this. Jenny does a great job.
Thanks dms. That's what I did for the last bag I made and it really made a big difference in the amount of bulk I had to sew through. I'm sure if I used 2 handles attached to the body of the bag it would have been a breeze to sew.
If I could only figure out how to attach a single side shoulder strap, I'd be fine!