add a metal box for your motor. And ground the box and your motor directly to the grounding point aka earth. Usually near your front gate.

really dont know what is the purpose of the foil. But I would remove it, silicon seal the the box to the wall.

The cage thing is to create a faraday cage. meaning that the entire circuit is in a metal cage/box that has no conduction between each other. The principle is simple but need some basic understanding, try google.

Grounding wise, you can try this: find if the earth point is within reachable, if not go hardware shop and buy a "earth rod" aka ground rod, it should be a 5-10 ft copper rod, and some bonding braid (if you made the box), ask for the one with pu sleeve. Hammer the rod into the nearest safe ground, without underground structure, piping and wire. For the box, connect it to the earth rod with grounding braid. For your circuit board, find the in coming harness, pick out the ground wire joint, split one more ground wire that connects the earth directly.

For maximum protection, add a surge protector between the mains and the circuit board. For this operation, you should ask your auto gate provider about it if your pcb burn again. He/she should had taken the bullet and add a surge protection. Typical grounding issue you are having.