You should attach the breakaway to the chassis of the car so that if the towbar becomes separated the trailers brakes will be activated.
I would however suggest that you have a permanent towbar professionally fitted to your towing vehicle as their have been a number of accidents were detachable tow bars have seperated from the towing vehicle.
In addition I would buy a length of heavy duty anchor chain and attachments so that you can wrap the chain around the trailers V bar and the chassis of your vehicle so that in the event of the trailer detaching it is still remains attached to the towing vehicle.
