some flies were elaborate custom made structures for wagons that set up on ranches at the gather/branding time where food was not only prepared butt served as the center of life when the cowboy wasn't "in the saddle"

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as seen above w/ some no longer manufactured/sold solutions most TTTnTD campers not only want the protection from sun wind and rain... they want to make a reasonably artistic statement where their solution is appealing and inviting from a distance

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folks w/ TTTnTD's are going to continue their quest of some artistic solution for wind sun and rain protection which will in many cases involve some form of providing privacy
since the chuck wagon was created from an already existing farm/ranch/freight wagon the means of storing and carrying poles was an external appendage of sorts frequently high on the side and consisted of a couple large hooks for racking the poles
IMHO racking cedar or pine poles on the side wouldn't quite be in order for today's TTTnTD's
SO... A solution to the OP's problem must begin in the planning stages of the build
consideration must be included as to how you plan to provide the needed/desired protections and where/how you plan to carry the poles necessary to support the structure whatever it may be/become
another consideration could be how you wish to attach/secure the structure to the trailer if you do
i'm seeing an under floor tray/compartment for the poles a/o the folded structure/fly
it could even be under the trailer frame in the elements ±
RV's use an extruded aluminium track that the awning bolt rope threads thru to maintain a waterproof attachment point on the vehicle
the track can be had by the foot or by pre cut lengths
using the track/bolt rope method would give the fly some added stability
a fly off the side or over the hatch or both could provide the desired protection
most big truck(18-wheeler) tarp manufacturers create custom tarps as their bread n butter
they have sturdy materials on hand and sources for most anything else one might desire
another source is the canvas products manufacturers that supply traditional/historical activities
i will be interested to see what thoughts others come up with
sw