Doff,
I mounted a box on my 2016 Fleet, but used a lightweight custom-made dry box rather than an Aluminess box. I didn't want to add a heavy bumper with swing-outs, although that would be the obvious choice. See photos below.
I've used it for two 4-month long summer/fall trips totaling about 25,000 miles, driving on all kinds of roads, and it has been great. It's absolutely rock solid and I've detected zero issues since the weight is well distributed across multiple mounting points and backed by fender washers and/or backing plates. I was concerned about adding extra weight beyond my bumper but I can't tell the difference (but I also have a custom spring pack from Boise Spring Works).
I use the box to variously store lightweight, bulky items (e.g., Alpacka raft, paddles, life jackets, backpacks, sleeping pads, sleeping bags, etc). The box and brackets collectively weigh a bit over 20 lbs and I never store more than 15 lbs in the box. I only use the water jug to fill my camper tanks when using a hose isn't an option, and it's always mounted empty. The box (but not the 2 brackets) is easily removable so I'm not always stuck using it if I don't need it. I'll add a couple more photos in subsequent posts.