Tom,

I think others have suggested pvc, and that would be my first choice also. 
Drill 2 holes at  one end and attach to the tower leg with a u bolt, or 
invent some  other attachment depending on what you have laying around.  Cut 
a slot into the  other end so the slot will be vertical  when the standoff 
is attached to  the tower.   Spread the  slit open and slide in the ladder 
line and it will grip it tight.

Have fun with the new rig.

73, Steve KW3A