I'd cut the platform all around, leaving 3 or 4 inches attached to the skirt. Then you could leave raw edges or bind with tape. Here's how I've been using for years now---slip the cut edge under the mattress and pin with lge safety pins around. You should be able to slide your mattress one side to the other enough to put the pins into the box springs. Makes it very easy to remove or change out. Believe me, it does not hurt your box springs at all. You can get the large safety pins that are curved for putting quilt layers together--almost anywhere. Makes for easier pinning. Just experiment with a bit of cloth before making the decision to order.

If the elastic stayed up okay without being fastened all around, why not use velcro at one corner? Cut off the platform and turn the edges under twice and stitch them. Cut a piece of scrap fabric about four inches square, and cover it with one side of the velcro, and stitch it to one end of the bedskirt. This would be the underlap.

Then put the other side of the velcro on the underside of edge that would meet up with it.

Thanks, I'm going to follow dancinggirl's suggestion. I looked around and did manage to find an old post on this subject Everyone likes the pin method. I will cut & fold double & just run a hem. I had some of what I call 'upholstery' pins which are the corkscrew type and I ordered another pkg. It sounds very do-able that way and able to handle by myself.

As for the other suggestion. I really did not want to add elastic. I didn't want to make a bulky casing which would add length to the bedskirt because it goes around the box spring on the outside, and I've never had good luck with sewing elastic directly to fabric without a casing. Especially because this will probably be a very skimpy fabric on the platform when it arrives.

I thank you both for your replies.
Donna

Do what dancigirl said, except use twist pins rather than safety pins. They hold forever w/o harming the mattress, and are avail. at fabric stores.

I have tried all these ways and not been satisfied. The problem is that I have a mattress that curves up and the platform, which is a different color and fabric always shows. We have a queen down comforter on a king sized bed and so the sides show. (my husband isn't into the looks of the bed, he just wants smaller comforter) And we have no top sheet to cover. And I hate the way they are making sheet now. Lousy.Hope you have better luck than I have had.