Have a look at https://www.amazon.co.uk/dp/B078KDB5K2/?coliid=I38H8IAJD1A397&colid=1WHPEC581TD5B&psc=1&ref_=lv_ov_lig_dp_it which is similar to The_Sleeper’s suggestion, but only £13.99.
You don’t want the chain loose, else it will shake around and rip the bag. It may be worth getting some kind of storage box, and strapping that down to your rear seat, or put the chain in the box and the box in a tail pack.