The Ikea bag from Amazon (Length: 28 ¾ " Depth: 13 ¾ " Height: 11 ¾ ") looks like a good choice if your back pack will fit in it. Mine did not. I would have preferred the Ikea bag if the size were right. Zippers could be a weak point but I don't know. Sewn in handles and back pack straps are a big plus. The Ikea and the Demo Trash Bags are constructed from the same material, Polypropylene which is very strong, it won't rip like other materials. 67% of the reviewers give it 5 stars.
https://www.amazon.com/dp/B00OS47EDK/?tag=casaivar02-20
The Highlander Rucksack Transit cover has a majority (56%) rating it at 1 star due to it's flimsiness. Many tear apart in air travel. It looks nice and is light weight (many of the travel covers out there are heavy and bulky, not something you want to carry 500 miles)
https://www.amazon.com/dp/B00872A012/?tag=casaivar02-20
Regardless of the bag cover you purchase, be aware if it comes off for any reason and your flight transfer destination tags are attached to it, you may lose your bag (see reviews on Highlander). Always have a copy of your personal information plus that particular flight information attached to your pack ALSO, not just the cover. I made up tags ahead of time for each leg of my trip and put them in a ziplock bag with the current flight info on top. When that flight ended, I removed the top sheet and threw it away exposing the sheet below with the next flight info, destination and personal contact info.