I am in the process of collecting a few parts to do more mods on my truck right now have a set of "FORD" Hadley mack truck horn's I was thinking to run Or I was going to run train horns, as for where to install them I would like to make a custom mount and put them either behind the grill so their somewhat protected or under the truck somewhere as a second choice, If I mount the tank under the box somewhere I might put the horns close to the tank
I just posted for the sounds guys not to buy theredoesn't really have to be that pricey heres a link to some good information for a starter.
http://stores.ebay.com/Siege-Engineering-Equipment/Questions-about-Air-Horns.html