I made an oversized king duvet cover many years ago to re-use an old and ugly comforter. I used GrannieAnnie's method to turn it, inserted the comforter by crawling inside of the cover to smooth it out (I'm sure that was a sight to behold!) and tied it with overhand double twisted knots through all the thicknesses. It has lasted all these years and we still use it. The "birthing" part wasn't difficult. You should give it a try, just be sure to leave a big enough opening to turn it. Some great advice about extra fabric in the ruffle corners and I wish I'd thought of using a broomstick! :-)