Thank you everyone for your advice.
I've taken the plunge and did the necessary cutting this morning. And it all appears to be going well.
I have machine-stitched one side of the binding, and just need to hand stitch it to the front and add the closure tabs (not integrated to the binding, but separate 'feature').
And then it will be finished, and I will be very pleased. I've only been meaning to make a tree skirt for about the past 20 years or so...
