Not sure the Trill and Scamp
have the same degree of bumper attachment to frame, scamp
as far as I know puts the tire on the rear wall so it does not need the bumper strength to support the tire.
My bumper is channel rather than tube but can't say that applies to them all. I would be worried less about the rack failing than the bumper welds cracking. If I was going to do a rack I would look for some location to add a little reinforcement to the bumper & frame. But hey I'm just winging it, and do have a tendency to overbuild.