SMS > GPS unit > Soundboard > Loud audio Message (all powered by 12v DC)

Hi,

I have a boat

There is a gps tracking unit on the boat

I am able to send a sms command to the tracking unit and it will send a current to any output wire I specify for 1 second

I have an Adafruit FX Soundboard : adafruit.com/product/2220

It has 10 terminals - with 1 different audio message assigned to each terminal

When i send an sms to the gps tracking unit to activate output 1 of the gps unit > current will be sent to terminal 1 of the soundboard and audio message one will start playing

The audio is sent out of the soundboard via AUX



Can anyone suggest a speaker that I can use to project loudly the audio from the soundboard :

I need the speaker to be :
- powered by 12v dc car battery
- can accept aux input from soundcard
- is loud (as amp etc built in)
- does not drain the boat battery by much unless it is activated by soundboard


Thanks .. if there is a better method to achieve the same thing without the Adafruit soundboard would love to hear it also. Thanks