In addition, since the container will automatically size to the width of the column when it initializes, you can "autocenter" the checkbox in the container's init.
this.checkbox.left = this.width/2 - this.checkbox.width/2
I haven't been able to get it to re-center when the column is resized, even using the Resize event of the container, so I set the column.Resizable=.F.
Insanity: Doing the same thing over and over and expecting different results.