Nice. I may have to check one of those out for when I need more storage. I use a Nelson Rigg standard tailbag with built-in bungees. On a solo trip, I bungee it in front of my passenger backrest backwards (taller side towards me) and it makes a great backrest. Comes with a rain cover that's never failed. It looks like you have about five times the storage capacity, though.
I'm with you on the top box. Never liked they way they look.