There are several threads on air horns. I recommend mounting it by drilling a hole thru the windshield (if you have one). The Stebel or WOLO Bad Boy (Harbor Freight, PEP Boys, u name it) can also be found in chrome for around $50.00 (Northern Tool).
This mounting provides a good height and maximum sound. Just hook it up parallel to your existing horn. I have had these models on 5 automobiles, GV, Xciting and Agility 50. I have also mounted the Hopkins Deer Alert (E-Trailer) to this horn.