I went and looked at the 2 car covers again at the shop today. Both are low buck unlined of different material. Neither of them are particularly soft considering they are on classic cars. I did look closer at the gathering. I don't think there is any elastic or stretch material in either one. The gather is across the front and across the back of both covers. The material is not very heavy...maybe like the weight of a light sweat shirt. It looks like it was bunched somehow at sewing. The stitch is very small...2 rows, like a double needle or some other machine for this.
I looked at a bunch of clothes at home and the closest I can describe is that it looks like the hem at the bottom of the legs of a well worn pair of jeans except that it is more stretchy. The material gives a little but I wouldn't call it stretchy. I also pulled up the fitted sheet on our bed...It definitely has elastic sewn into it. My wife commented that it is hard enough to get me to help make the bed and now I rip it up just to check out the fitted sheet.
Anyway, is that really correct....1.00" dia ??? that sounds pretty large. I do like the idea of the shock cord. I saw some on a spool at Tractor Supply. It was really light, much lighter than bungee cords.
There is so much to learn...how am I ever going to do this??