Those Stebel horns are popular for bikes. It's basically a mini air horn. Gotta be careful not to ingest water into the air intake though. You can separate the pump from the horn as well. Then you can mount it just about anywhere. There is also a marine version that's all white.
My problem wasn't loudness but the tone. Only having a high horn sounded a bit too frail. The Wrangler S's all came with a single horn unlike the higher models which came with dual horns.