I finally got tired of making do. The T-shirt bit worked ok(ish) but was often a pain and the DIY comando cloth wasn't much better. I now have an Original NOS Kodak dark cloth which is super simple and ridiculously light. It's handy for when I'm trying to keep the weight of my kit down. They pop up from time to time on eBay for reasonable prices. I also have a nice handmade dark cloth from
https://www.wandererphotogear.com/ . Double sided, with a really nice light colored fabric on one side and black on the other. It's pretty light tight but breathes which is why I wasn't down with the BTZS cloths. It also has a nice elastic drawstring which makes it easy cinch down without fussing with velcro.
One modification I made to my ToKo was to glue on two large washers (one on either side), to which I added two neodymium magnets. Works great as a simple clamping mechanism without adding a boatload of complication or fuss.