Hmmm. I looked at the photo of the trellis support on the website and it seems that it is a weak design.
It says that the trellis support also secures the tray so you cant really mess with it.
Maybe PVC would be more rigid than the conduit?
Looks like you may be able to drill hole and secure with a screw or clamp at the base of the trellis support where it latches onto the lip of the tray to prevent it from moving it up and down.
Just throwing ideas out there ... perhaps you need to create some cross supports between the vertical trellis supports to stabilize the structure and prevent lateral movement and keep your lengths of trellis shorter than 50 feet. Say, Five ten foot long sections instead of one 50 foot section.
"Mark ye, be forewarned; Ahab's above the common; Ahab's been in colleges, as well as 'mong the cannibals; been used to deeper wonders than the waves; fixed his fiery lance in mightier, stranger foes than whales.'"