I finally got around to making an enhancement: I twisted a coat hanger around and made a garbage bag holder. To finish it off I coated it with the stuff that's used for covering the handles of tools. I did two coats on the whole hanger in stages. On our recent trip it performed very well.
This is what it looks like up close:
And this is it mounted, ready for a trash bag.
x-posted in a slightly different form to eor