Better questions will yield better answers.

You do realize that there needs to be some additional information from you.

There are plenty of audio amplifiers suitable for 12VDC operation. A research visit to a local "pimp my ride" shop is called for.

The larger the audio amplifier, the heavier drain on the engine and the higher the fuel consumption. Also, the bigger the nuisance to the local community. In the UK, vehicles have noise limits imposed upon them that are frequently disregarded by the "boom boy racer" brigade.

Bear in mind that such modifications to a vehicle are notifiable to the vehicle's insurers and that a higher premium may be due.

I have heard there is a cat with a cross bow enforcing these regulations.

Possibly.

Sure "Guest"! How many Megawatts at 27 MHz do you need?

Pardon the joke if you will as there is a lot to specifing a mobile communications amplifier. First off we need to know what country you are in so that amplifiers with the correct approvals can be recomended. Next the frequency and type of emission (modulation) are necessary, and finally, what power output do you think you might need?

Have FUN!
TT3