I used the trap wires for balance purposes a few times. IIRC i tied to the cornercastings rather than to the pylons. I did not include much slack in my setup, since the pylons are in line with the mast base. There is a slight difference in height between mast base and corner casting. This is the amount of slack I would be aming for. In my setup the lines and the knots allowed for some "elasticity".

Howard... this is just a temporary setup while stepping the mast. Once the mast stays up by it self. He will use the shock cord to connect the two sides of the trap wire.
Patrick