I'm getting a "wild hair". Have any of you, that are towing travel trailers, installed "Air Horns". The type that have an air compresser and a tank reservoir. I haven't looked under my "truck" to check for frame mounting and so forth....I was just looking at a set of really loud train horns........

 

I did it.
I bought an air horn kit from Rickson Truck several years ago. This is the third SUV I've had this system on. On my 07 Expy, I mounted the air compressor in the compartment in the rear on the drivers side where the fuel cutoff is. From there it is plumbed to the reservoir mounted underneath by the spare tire. There is a solinoid valve mounted on the reservoir that is plumbed to a twin trumpet horn that is mounted on the side of the frame rail on the passenger side underneath and between the front and second row seat. It is well concealed and protected there. I mounted a foot switch on the floorboard that I can activate with my left foot.

 

Does it play Dixie?

 

Naa...Berry, they just get real loud when towing a trailer and some **** decides to cut you off or see's how slow they can enter the roadway when the tow vehicle is bearing down on them. Good one's will get their attention.
By the way, there is a way to actuate them from the oem horn button.