For my 4x5 I use an old black t-shirt. The neck fits snugly around the camera back and there are sleeves on both sides to put a hand in with a lupe. And folds to pocket size.
I have the 4x5, 5x7 and 8x10 versions of the BTZS cloths from Fred at the View Camera Store and I agree, they are very good. The 8x10 version I feel like could be used as a shelter for myself and the camera if I ever got caught in the rain it feels so large. The other week I was out of the road and realized I forgot to pack my BTZS cloth for the Canham wood 5x7 I had with me so I made an emergency stop at Wal-Mart and was able to find a two-pack of 63x37" 100% black-out panel curtains. I thought it was just going to end up being for that trip but at $6.95 for a two-pack, I keep one in the car in case I forget to pack a cloth in the future. The black-out curtain panel ended up being easier to use with the Canham since I didn't have to worry about the elastic getting in the way of the rear shift and swing levers that stick out the back of the Canham. I was very impressed with that simple solution. The only downside of the cheap black-out panels is they are not waterproof and I'll have to add some office binder clips to clip them on the camera when it's windy out. They do fold flatter than the BTZS cloth though. It's good to have two solutions available.
I have a Blackjacket from QuietWorks that I picked up used on Ebay. It's not super-light but it packs down well into a small bag, it's sturdy and weighty enough to not blow around in the wind, and it has handy sleeves for arm access whilst still keeping everything dark. It has a couple of elasticated adjustable cords to fit around the camera. My only gripe with it is that, even though it has a silver coating, it can get a bit hot inside on warm days.
I started with the 4x5 dark cloth from Fred Newman, and found it too small for the back of my 4x5 Chamonix. The cloth has an elastic that wraps around the rear standard and it kept coming off when I tried to do movements of the rear standard. I struggled with it for a year, and then decided to get the 5x7 version, and it works great for the 4x5.
The dark cloths I use come from Wanderer, who makes them in a wide variety of designs. They have both normal and "ultra light" versions. (Yes, they're a bit pricy.) I started with a regular one, but switched to an ultra light because I kept having issues with the ground glass fogging up due to sweat/condensation when I used the regular one.
I have both Harrison and BTZS are both great dark cloths. The only problem I can see with a light weight cloths is that light wind will cause it to blow around and make it difficult to view. Have you had this problem?
Do you know where I can find a female bi-port to PC sync cable I can connect my Wollensak Pro Raptar 210mm F5.6 to my flashpoint 600 trigger. Any suggestions?
I got a 1.2m x 1.2m (4fx4f) blackout fabric on Amazon for £6, and added poppers to hold it in place once I wrap it around the camera. Total cost was under £15