I hadn't thought about the mounded beds drying faster, but I bet they do. I built them years before I knew about hugelkultur.If you are just mounding soil up for a raised bed, do you find that the soil dries out faster than level, in-ground soil? That was my experience with my first raised beds where I did not use the hügelkultur method for the build. For me, it worked much better to add that wood in the bottom of the raised beds.
Like a lot of things, wish I had known then what I know now!
Since I'm not going to dig them out and redo them, I try to mulch HEAVILY with leaves, compost, chicken run material, grass clippings, whatever I can get. I'm hoping the metal on the sides will give me a firm "border" of sorts to contain water when I need to water them, and to keep the best of the soil on top.