I've done two installs on my sons' trucks. On the '05 Chevy the horns are mounted behind the front bumper. It has a three horn common manifold style set up (Hornblasters Jacka$$) and the compressor and tank are mounted in the bed on the wheel well. The other was a 5 horn set up that you have to figure out yourself (Hornblasters Conductor). That one is on an '01 Dodge dually and everything is mounted under the bed. The horns themselves are mounted where a spare would mount and the tank and compressor are mounted upside down to the bed itself.
The horns that are mounted together on a manifold are easier to mount and generally they're smaller. The 3 horn also uses a combo tank/compressor that are mated to each other. The 5 horn set up is individual horns and all together they take up much more room as well as requiring a larger tank. On this one the tank and compressor are separate and are just mounted near each other. Some of the kits do use tank mounted compressors, but my son wanted a larger tank.
The 3 horn is really just a very loud horn whereas the 5 horn horn has a true train horn tone. The smaller one is definitely easier to mount. I had to fabricate mounts for both systems, but the 5 horn was alot more work and takes up way more space.
These were not plug and play, but if you're not afraid of some fab work it just takes some imagination and time. Measure the spaces that you think you'd like to mount things and check the dimensions of the components. The pictures are deceiving on how large some of the horns really are. On the Chevy my son decided he wanted the train horns and when we got them there was no way we were gonna mount them unless we put them in the bed. They were huge and we ended up returning them.
