I suggest making a separate box collider so in code you can grab its bounds. Then find a random position in that box to spawn an explosion every .2s using a coroutine. At the end of the coroutine, I scaled up the finale explosion!
Also, the sounds are quite repetitive if played in quick succession. Another suggestion is to modulate the pitch by a random amount by each time a particle is played. After realizing the difference this made in making things sound more natural, I’m going to have to make this into something modularized so I can apply it to any repeating noise like a blaster or footprints. Try it out for yourself! (Be sure to reset the pitch if other sounds are using the same AudioSource!) Good Luck!