I ran into a problem with a specific color of thread for one of my bags in this project, but I quick came up with a solution. I took some un-waxed cotton thread and carefully dipped it into some dye for the color I needed. I inserted the thread and closed the cap to the dye bottle. I shook it vigorously until I felt that it covered all of the thread good. I then removed the cap and carefully pulled the thread out hanging it allowing it to dry. Once it dried, I used a piece of paper towel to make sure that the excess dye was removed. I then applied wax to the thread and proceed to use it for stitching.
I applied contact cement to the perimeter of the gusset and carefully attached it when the glue became tacky. I used 'alligator' clips to help keep the gusset in place while I worked around the area. I then punched my stitching holes and stitched the first gusset before I proceeded to the second one.
I repeated my process for attaching the second gusset. This was repeated for both bags.