Here is the link to the bag:

Orford Rooftop Cargo Carrier，Waterproof Roof Rack Cargo Carrier Bag, 15 Cubic Feet Black Car Top Carrier https://www.amazon.com/dp/B07FNGMTZZ/ref=cm_sw_r_cp_apa_i_9ikiDbFDFG9RT

It was originally $20, if I remember correctly.