Hi Michael,
The soft part of the velcro set goes on the inside of the wrap and the hook side of the velcro goes on the outside--I imagine the hook side of the velcro would be abrasive to whatever you are storing inside the wrap.
I start by sewing soft stretchy cotton fabric to some upholstery fabric--front/right sides together for turning inside out. I cut the material 9" x 9"--for the smaller lens wraps. The resulting size is 8" x 8" with a half inch seam allowance around. I sew all four sides, except on the last side, I leave two or three inch opening so I can turn the fabric inside out. (UPDATE: this opening should be in the middle of one of the four sides--all corners should be sewn with the sewing machine before turning inside out. I was sewing all but one corner and that is stupid because it's harder to fold in the fabric--after you turn it inside out--on a corner than the middle of a side.)
I trim the seam allowance down close to the seam I just sewed all the way around (leaving a little more of a seam allowance near the opening).
I turn it inside out pushing the corners out with a pen or a long stick. I flatten it out as best as I can and start stitching right around the very edge. For the opening I turn it in by hand continue stitching over it along the very edge, continuing the outer edge seam.
I then use a ruler and draw two lines, from one corner to another, making an X. I sew along these pen lines. The reason I do this is to keep the inner fabric in place so it wont shift around. The storebought lens wrap had this, so I figured I should too. You could use some thread other than black if you like--to help match the fabric--but I just made it easy and did it all black since I need black thread to match the black velcro pieces.
I just bought the sew on velcro since it is less money than the adhesive. You'd have to sew it on anyways. I guess there is iron on as well but it costs more and I don't know if I'd trust that as much as a seam. I imagine the adhesive would help keep it in place while you sewed it but I didn't have any problem using my hand holding it in place as I sewed it--after you start the seam it pretty much holds itself in place anyways.
I put the velcro pieces on with them slightly hanging over the edge of the wrap. After they are sewn on I trim the edge with scissors to make it flush with the lens wrap fabric.
For the 8 x 8 wrap, I use 3" long pieces of velcro (for both the inner and outer). for a 11 x 11 wrap I use 4" pieces.
For the outer fabric I'd recommend canvas, something thick and/or waterproof, or some upholstery fabric. I got some upholstery fabric samples (18 x 18) for 25 cents a piece on clearance--they were like $30 a yard.. so it's some nice fabric
Check the remnant bin in Jo-Ann's for upholstery fabric--fabric is like 1/2 off in it. I just bought 1/3rd of a yard of $19.99/yard upholstery fabric from the remnant bin today at Jo-Ann's, half off, for only $1.73. I made a lens wrap from it and have enough fabric left to make like 3 or 4 more--but I want different fabric for every wrap so I can identify them easily. I'll end up using extra fabric for something else I'm sure.
I love sewing
I'm saving a lot of money since I learned how and the machines are affordable. I got a singer 15-91 for like $60--mine made in 1955--and it's built like a tank (30 lbs) and looks new.. put some car wax on it the other day