On the Tantrums, have you tried turning off the lights, changing the room temperature, or handing him a heavy blanket to wrap himself in?

Basically change his current sensory situation to see if that stops what is overloading his system.

For me, my friends and husband know to start with the lights (if I am stunned), then try raising the room temperature (I get cold easily), and then just throwing blankets and jackets at me (temperature raising and sensory pressure helps me center my self).

If those don't work, I have an "off switch" on my right shoulder blade. If someone presses it hard, I completely shut down for 30 seconds to 5 minutes and when I come back I am mostly fine.

Additionally, if there is a lot of noise in the room when your son is melting down, I reccommend turning off what you can, asking people to whisper, and moving your son to a more quiet location.

Does your son have a dark quiet place where he could go hide if he is overwhelmed?