2x2 lumber. I measure out the space in-between poles and then drill a hole the same diameter as the tent’s piping. I cut this down the middle resulting in a 1/2 “moon” as it’s 1/2 of the hole. This slots perfectly into the upright piping supports and is held in place with quick-ties secured via a small hole drilled in the 2x2 just behind the 1/2 “moon”.
Cheapest option I’ve come up with and it allows for multiple mounting points along the walls!
In the above pic you can see I use these braces to support supplemental under-canopy lighting (3000K led shop lights).