Ah @crafter you haven't taken account of numptys like me who can't do zips
A cushion cover would be a good place to practice because it's a straight seam and you can work on it flat. Try it out, you will an expert in no time.
"Then sew up the other three sides - "
Remember to leave the zip open...ask me how I know...
Should have mentioned that. We've all done it - once.