I mounted my brackets just below the floor line using all stainless steel hardware with nylon lock nuts and washers on the backside. It's been working great-to-date.
One thing I did which is a good/bad thing. I mounted the brackets spread apart farther at the bottom than straight down from the awning.....like spreading your legs for improved side-to-side stability. The issue is that they don't just drop into the brackets because of the slight angle of approach. A moderate push and they are locked in tight. If someone tries to help, they don't have the touch to hook in or out. Like I say a good/bad thing. If I had it over, I would still spread them, but not as far.
For those who don't know, these are nylon lock nuts.