Our first trailer (Boler) didn't have an awning rail. But, for some reason, the previous owner had installed a couple of eye bolts through the belly band on each end of the trailer.
What we did for an awning:
I bought a cheap self-supporting awning from K-Mart (I swear, I think it was something like $5 for a 10x10 awning. Has a pole in each corner and one in the middle.
On one side of the awning, I just laid it up on top of the Boler
tying lines to the corners which then tied into the eye bolts.
From this point, I'd just set up the rest as originally intended. Pole on each corner with lines to the ground. Pole in the middle.
Sure it's not as fancy as PVC plumbing...
but it got the job done for $5.
I may actually have to recreate that (or something similar) for the Amerigo
I'm working on. I'm not sure there is room for an awning rail on it. There's VERY little room between the top edge of the drip rail over the door and where the roof starts to curve to the roof. Not enough for an awning rail I fear. So I may be stuck doing some sort of clever alternative instead.