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In a pinch I used something like this I had in the garage to hold my bag off the back wheel: [https://www.amazon.co.uk/RIO-Direct-Tensioning-Adjustable-Motorcycle/dp/B08FJ161RL/) - it actually worked pretty well and was quite light. I think the one in the link is bad quality, but there are lots of others if you search 'tie-down straps'
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Basic cinch straps instead of a Voile? ie. those things you'd see on a backpack
You can get velcro and non-velcro ones.
Something like: https://alpkit.com/products/dual-straps-grey
Just packing for my DIY TnR ride and I've fitted a dynamo and light so I don't have to worry about power to devices (or light if I ride early or late). Anyway, the tent/mat/quilt bag is sagging the harness a bit like usual but it's resting on the light but I think a voile will sort it out. Finding a long enough voile strap I can get in a week is a challenge, any ideas what else I can use?