Concern with attaching bike rack to TT bumper

Well, to each their own, I suppose. Depends what you're riding and how important it is to you. For me, I don't want my bikes bobbing on the rear end of a TT on a rigged contraption. I prefer a hitch mounted tray rack on the back of my vehicle, but when that isn't an option, on the roof is the next best place IMO.

But I like my bikes a lot more than I like my TT (or just about anything else I own, for that matter), so they get preferential treatment!