I found that only Lowes had a largest enough fence post to fit the folding ladder. They sell a few different fence posts, but you'll see one that has two rectangular holes cut into one side for inserting railing. This one is big enough for the ladder.
The reason for the fence post use is to keep the ladder up off the floor and easy to access without having to unload have of your bay. On my last two DP's, I mounted it as high as I could in the pass thru bay where the adder would still clear the bay door.
Mounting......I found that adding a couple of pieces of wood to the wall first, like a couple of 1"x 2" x 6" pieces made mounting easier. I then drilled two holes in one side of the fence post that was large enough to fit a large wood screw and flat washer though, so that I could then go through the tube and screw through the opposite wall into the wood blocks I installed.
Don & Mary
2019 Newmar Dutch Star 4018 (Freightliner)
2019 Ford Raptor