Ed, I'd bet that it would fit the Hondaline top box for the NT. In fact, I wouldn't be too surprised if those boxes were the same part number. I'm using a $12 duffel bag I got at Walmart and it works great. I pack it with clothes, shaving kit, etc. that I take in every night while I'm traveling and have room in my CooCase for my netbook in its case plus my thermos of coffee and my Kindle.
I also have the big pannier lids and use the the right pannier for tools, tire repair stuff, 1st aid kit, etc, and the left one for other clothes while traveling.
Works for me.
I do have Honda's bag liners for the panniers, and they are very likely the exact same thing Bestem sells. They're good products and I wouldn't have any issues with trying the Bestem trunk liner if I had seen it. If you try it, give us a report.