Here's an interesting idea I just found. REI has these on sale for$45 (normally $99). Compared to the Sierra brand at over $300, this is worth checking out. You have to put it in your cart to see the extra 25% off.
https://www.rei.com/product/882939/evrgrn-crash-sack
https://www.rei.com/product/882939/evrgrn-crash-sack