Shug has a few videos that spell it out also. You'll learn some things and be entertained, both are good, right?
I tried using thin cord to corners and found a sagging UQ which meant cold air leaking in and the dreaded CBS, even with cinches on the ends. I stitched in a channel along each side, ran shock cord through them and secured to the gathered end. It made a huge difference in comfort and I was toasty warm.