I'll try to find pics later but I mounted my horns in the front grille. Two directly to the radiator support bracket and two to a flat aluminum bar which I attached to the same bracket. I mounted the compressor to the frame rail and attached a piece of diamond plate of aluminum underneath the driver's side rear passenger seat. I bolted the tank to the plate. The compressor and tank should be mounted near each other if possible. If you don't have a spare tire underneath, some people will mount the horns in that cavity. Wiring the switches and valve is the hardest part of the job. The horns can be mounted facing in any direction but I would personally advise you to mount them facing down or to the rear. Facing down makes them very loud because you get a shockwave off the pavement. It also keeps water from getting into the horns. Any way you mount them will be loud though.
07.5 GMC LMM SLE2, Z71 ECSB, ReadyLift 2" Kit, EFI Live-Autocal DSP5 by Idaho Rob, Magnaflow 4" downpipe back stainless exhaust w/DPF delete, Banks Ram Air Intake w/Super Scoop, Airlift 5000 Airbags w/In-cabin controllers, Retrax Tonneau Cover, Shocker Train Horns with 5 gallon on-board air and Viar Compressor, Bilstein 5100's, Line-X Bedliner, KMC XD Series "Hoss" Wheels, Mickey Thompson Baja ATZ's 285/70/17, B&W Turnover Ball