Just an FYI, those air horns use a lot of air. So, by the time your done "tootin" your horns, you may not have enough to fill tires up. I have seen these installed in commercial trucks and have seen the air pressure gauges for both tanks go down quick.
Installing a CTIS system would be awesome. Our big trucks in the AF had them (5 tons and 2 1/2 tons). They were sweet. They had 4 different settings. 1) Highway which had them at normal pressure. 2) Sand, which aired them down quite a bit. 3) I don't remember ahahaha. 4) Runflat. If we punctured a tire and it was losing air we could push that button and it would direct all spare air generated to keeping that tire inflated. Never got to use that button.