I will be installing my Nathan P3's (real train horns, not the plastic ones) on my 2007 Tahoe in the next couple of weeks. I've had this entire setup on 4 different vehicles ('08 Tundra, 06' white TBSS, '08 Denali pickup, and '06 blue TBSS), so the Tahoe will be the 5th. The easiest thing to do is remove the spare tire and all the associated hardware. With that stuff gone, there is plenty of real estate to mount your hardware.
My setup are the horns (Nathan P3), a 5 gallon Hornblasters 8 port tank, Vaair compressor, and a SMC nickel plated valve. All of this stuff fits with no issue with the spare removed on all 4 previous vehicles. I use 18ga angle iron to help support the larger stuff, usually routing it through and/or bolting it to existing chassis points that are drilled by the factory or by me. Mind you, the zip ties you see in my photo are not what support the hardware, they are took take a little shake or play out of the horns and other pieces to keep them from moving around too much.
Here is a video of the Nathan's in action on my Denali.
