Another alternative to a traditional dark cloth is black or dark t-shirt.
Get an xxl or bigger (as many x's as you need for the body of the shirt to fit around the back of the camera).
Put your head through the neck hole, stretch the body of the shirt over the back of the camera. Drape it over your shoulders between shots. Compared to a regular dark cloth the t-shirt is more compact, and gives 360 degree coverage without a lot of extra material. The slight stretchy-ness of the knit keeps it in place on the camera.
You don't really need velcro, etc for the dark cloth, just drape it over the back of the camera. IMHO stuff like velcro makes them too fiddly, it sticks when you don't want it to, to stuff you don't want it to stick to, and doesn't when you do.
I have one ready-made Calumet dark cloth which has the white and black sides. It's kind of a pain because the fabric is very slippery and it doesn't stay in place, though it is noticeably cooler when working in the sun. The ones I have that are just a plain piece of cloth from the fabric store work better over all though.