For this creation, I've cut out strips of fabric, folded it, so that the edges meet, on the backside, upon which I've sewn it, using an elastic seam.
Then I've 'constructed' the cock and ball holder, making sure that it stays tight when I'm erect, and have let the rim in the middle-front continue down around the ballsack, tight enough to grip it, but not so tight, that it divides the balls.
Inside the waist-rim, I've added an elastic ribbon, in order to supply the 'grip'.
Click the pictures, to see them full-size.