Tony,
I successfully installed the tower following Mark Erdos's methods.  There were only two differences that I implemented to make the arch stiffer to lateral wobbling.  1) Instead of making the width of the arch longer than the distance between the arch legs, as recommended by the manufacturer, I made it shorter and stretched it to create tension in the opposite direction when installed.  Before doing this I had a long discussion with the engineer from Atlantic Towers arguing that this type of pre-stretch yielded greater lateral stiffness than the method they recommended.  He agreed with my statement but told me that users preferred the look of a bowing-up arch instead of the bowing-down, which was of lesser magnitude when stretching outwards the arch legs.  To me, the lateral stiffness trumped the bowing look 100 times.  2)  I paid extra to reinforce the corners of the forward arch identical to those of the aft arch.  It was not cheap, but the result was a substantially stiffer arch that did not need to be stiffened with cross cables during passages.
Like Mark, I dont carry the dink on the arch except for short passages.  Pix below: