I have used both, and I think the hitch mounted basket is the way to go. The car topper just created too much drag and it bothered me when driving, plus it's hard to get at in case you need something mid-trip. In 2008, we used a hitch basket and then bought a big locking tub (rubbermaid?, it is heavy duty grey and red), it was great and yes you might need to be careful parking, but driving a big vehicle like yours, you are already used to that. We stopped halfway, so I actually used a bike cable to secure everything to the basket, as well as a locking hitch pin...worked great and I could leave it while at the hotel...also securing the load for the road time. After we used that once, I sold my car topper, there was no going back.
I did add more reflective tape, the reflectors that came with it just didn't seem sufficient.
Just be sure that your load is positioned (my rack has a low and high position) so that you can get your lift gate opened while the stuff is still in the rack.
To be fair, our car topper was not one of the newer sleek looking ones...but I can't imagine those hold much.