Horns are 157 decibels. The entire system is mounted under the bed in the RF corner, space between RR wheel and front of the bed. Compressor is mounted up high, tank on the frame. I have 2 trumpets, they are not "ganged" which gives you more options for mounting. They point forward and downward.
I just upgraded my compressor today with a massive much larger unit and a larger tank, now run 1.5 gallon tank.
Mine is all in an area where nothing is in anyone's way if work needed to be done. I still have my spare tire (see people remove spare to mount 5 chime train horns, dumb...)
I have it set to work with a key, but have a manual off switch and a push button for the horn. They are a lot of fun. People pay attention.
Stay away from the tank/compressor units, get them where they are separate. Make sure the compressor inlet can be piped to suck clean air from inside the cab via and air filter. You can get pieces and build your own, probably the best option.
hornblaster 2 trumpets are perfect.
PM me or ask my any questions on this thread in case others are also curious.
Then look for a tank, 1 to 1.5 gallons. Here is a decent kit.
I just upgraded to the 200 PSI compressor, but had the above one for years with zero issues.