I made something like this a while back while experimenting with different Tunisian crochet stitch patterns. Depending on the gauge and stitch pattern, Tunisian can have a strong tendency to curl. At some point I worked a very tight, very curled little swatchlet, and in a stroke of inspiration used it as a zipper guard for knitting with a ball of yarn in my bag. But since the original was made out of fuzzy acrylic yarn, it would snag on the yarn passing through, and eventually I stopped using it.
King Tut is a very smooth, mercerized cotton yarn, much less likely to snag, so it is better suited for this use.
This pattern turns the advice for avoiding curl right on its head. It uses a relatively small hook (G/4mm) and a stitch (Tunisian Knit Stitch) with more bulk in the back then front. This causes it to roll into a tube, which you can then slide your working yarn into from the side.
To make it, I started with 8 chains, picked up Tunisian Purl Stitches in the back bump of the chain, then after the first return pass made one more row of TPS + return. (I wanted the very first bit to be flat to provide some structure to the tube.) After that I firmly worked rows of Tunisian Knit Stitch until the fabric was long enough to roll over into a tube. I finished with a "bind off" of *TSS (Tunisian Simple Stitch), yo, pull through both loops* across, then worked regular crochet slip stiches along the top and right sides to add a little more firmness. I also added two lines of slip stitch on the back, to make a space for the zipper to slot into. This used about six yards of yarn in total.
If you
don't want your Tunisian crochet to curl, here are a few articles on keeping things flat: