I found a Market Umbrella on sale at Sam's Club for $80. The 10ft umbrella doesn't give as much total shade as an
awning but, with a stand, the shade can be positioned wherever you want. It seems like most of the interior heat comes in through the
windows, so I especially wanted to be able to shade those.
I had originally thought I'd have to mount some sort of a bracket on the rear bumper, so the umbrella would clear the A/C unit. But a previous tenant at the RV park left behind a couple of umbrella stands and that seems to work perfectly. The umbrella is one of the fancier commercial models with a tilting head and cranking in just a slight tilt is enough to clear the A/C (see second photo).
After these photos were taken, I snugged it up against the rear bumper behind it and right up against the spare tire on the side, then bungeed it to the bumper and used a tie-down to secure it to the spare tire. This seems to work in
light gusting winds. The alternative would be to add some weights to the base, but you have to be able to move it away from the trailer to be able to raise or lower it, so bungee cords will let you get by with a lightweight and easily moved base.
So far I'm quite pleased with my "awning." It's not as fancy as the factory option, but it's much more versatile and cost a
lot less.