I wanted to bring this thread up again as I tried to install my supertones without removing the bumper like OP did.
Maybe my arms are too thick or hands too fat, but I found it 100x more difficult to try this method versus taking off the bumper. Even wioth the Subimods bracket and harness, I found it impossible to fit it on without taking out the OEM meep-meep horn which itself was impossible for me to take off without removing the bumper first.
I personally suggest everyone save themselves the trouble of using OP's method and instead just use the iwsti how-to-guide on removing the bumper and do the supertone install with the open space. Also it allowed me to much more safely ziptie the harnesses where I can see clearly where it won't freely dangle and come loose in the elements. Removing and reinstalling the bumper was quite easy, much easier than trying to do everything through the lower air-dam.