I tried for as straightforward method as possible for a bug net on my Hunka XL and the result was this:
The aim was a net that would close completely to keep slugs and earwigs out, wouldn't restrict the opening of the Hunka for getting in and out and would still allow the hole to be adjusted.
I used a 72" by 9" length of mesh and 36" of 20mm velcro that I already had in my bits box. A zip would be quicker to close than velcro unless the material got caught in the zip and I've had that happen before.
The mesh would have been from either Pennine Outdoor or Point North and the velcro I buy at a haberdashery. There was no need to hem the mesh because it doesn't fray when cut. It is very slippery going through the sewing machine and puckers easily, but a no.80 needle, with normal tension and stitch length, solved that and also went through the Hunka material without any trouble.
Sewed the velcro onto one edge of the mesh first and then sewed the other mesh edge to the bag making sure to stay between the stitch lines of the fold over that the Hunka closure cord runs through. I didn't want the closure cord to get caught by the stitching, and I wanted the cord ends to end up inside the bug net so I could adjust the opening without having to open the velcro. Finally, sewed the two short edges of the mesh together.
As I pull the cords in, the mesh seems to stand further away from my face because of the stiffening that the velcro provides.
The Hunka still folds into its stuff pocket and suffers a weight increase from 574 to 592g.
I will be dumping my head net (a large Exped mesh bag) and taking the bug mesh from out of my Bear Paw lair to compensate.
If I was doing it again I would make the mesh 8" wide and the velcro slightly shorter so the opening tapered down a bit. Eighteen grammes, however, isn't enough to make me want to unpick it. :)
I hope this is of help to anybody thinking of doing it.