Scrapdunes, despite the name, have nothing to do with the battle arenas know as 'Desert Scrap' or 'Battle on the Dunes' but instead have to do with the mass junkyards theorized to be scattered through the world.
These 'scrapdunes' are said to contain meaningless junk and worthless trinkets, if an adventurer was lucky (or daring!) enough to find one.
These untold treasures of mediocrity have never been found (be it because they are hidden so well, because they don't exist, or nobody has ever looked for them, nobody knows for sure), so 'Searching for scrapdunes' has become a common idiom among the people, meaning 'putting a lot of work into something that reaps no reward'
Bell-hopper