ok i bought a sub/box/amp combo and the amp was attached to the box, well the amp didnt work so i had to get a new one

now my amp is just laying on the trunk not attached to anything. i'm afraid having it shuffling around back there will be bad.

should i mount it to my seatbacks? and if so, how? how much would an audio shop charge to install it there? everythings wired up and the sub works, its just the amp isnt mounted

thanks for the help