Adding a train horn/air setup for your Tremor sounds like a fantastic idea, especially if you're already considering onboard air for towing. HornBlasters and Klein both offer great options with fantastic sound quality. Concealing the horns might be a challenge due to the smaller space up front, but it's doable with some creative installation.
One suggestion that might fit your needs is to consider a drill train horn for a more seamless installation. It could potentially help with fitting and concealing the horns without requiring a spare tire delete kit, keeping things neat and functional.