Well, you say you're prepared to go 120 volts, whatcha got?
The supplied specs say 80 watts but that's horsehockey. It can draw more than that.... I'd say at least 3x what they say so a 300 watt continuous inverter would be able to handle the power draw. I wouldn't try to mike up an entire Heavy Metal band with it but as a PA "engineer" I'd say it would do the job. An all horn setup would sound "honky" and have a tendency to feedback. The 10" speaker with a piezo horn will give the announcer a more natural sound and if you want to play music between racks then that would sound much better.
https://www.musiciansfriend.com/acc...b9760b-exterior-mounting-bracket?rNtt=speaker mounting sockets&index=7 You would need 2 of these. There is a link in the ad to other mounts. They require a hole to mount the socket in but in my opinion it wouldn't be needed as the weight of the speaker is very low. The socket-type would hold up to a cabinet with 15" speakers.
https://www.musiciansfriend.com/accessories/proline-lst2bk-speaker-stand-pair
What I am showing you here is all new stuff with guarantees unlike used eBay stuff and comes in under $300 with free shipping. I have dealt with these guys for years without a problem. They ship fast, nearly as fast as the legendary SEMROC shipping times