Doc, mine has a telescopic radio antenna like the ones cars used to have. Only difference is that it's mounted on the side of the trailer, with two blocks. It's just behind the window guard on the streetside.
For flag holders, we use the ones like you see people use in a car window, with a mount that slips over the glass. Ours are actually from Harley, designed to slip over the rear of the tour-pak, then you close the lid on them. But I think they're the same thing.
At any rate, I lift the top of the propane cover, slide one on each side of the cover, then close the lid. We have a flag on each side of the propane tanks.