Patio umbrella pole insert

My first make was for a coworker who asked if I could make him some new inserts for the poles of a patio umbrella. I've never seen the umbrella, but I understand that this part fits into a pocket in the fabric of the umbrella to keep it in place. There were two different sizes, but only the small one is included here. I was told that my prototype of the large piece that I made before I learned how to use hull to round the edges was good enough. This was my first time using OpenSCAD (or any CAD software), so constructive criticism on how to improve it would be welcome. I didn't think to take a picture of the finished product before I gave it away.