A:
2 ways:
The most common is tu cut about 6mm of tubing and insert the eye of the hook inside. Afterwards, pass the eye of the hook on your main hook. This will maintain the trailer hook in a firm position.
The other way is to insert the eye of the trailer hook in the main hook and then put place the tubing across the main hook (but not by the hole, but perpendicular) this will let you have a loose trailer hook but I would recommend tubing with less diameter.