I think Meryt is right, fruit trees can last a long time, and it's also the sort of thing that's touted on sales sheets. How about a grape vine or two, on a nice salvaged-wood
trellis? A hardy kiwi?
I would expect sticking with fruits that non-permies will recognize would be the best way to keep the appeal broad; then, if you happen to rope in someone who seems interested, you can start talking companion plantings, guilds, etc. Speaking of companion plantings, some flowers to spruce up the yard can't hurt... and if they just happen to attract beneficials/repel pests/build soil...
I would think the sales appeal of hugelkultur beds might be a bit limited in general... but right along the
fence as you describe might not look too weird to the normals. You could slap some lumber across the front and level the top, and tada, a conventional
raised bed!
What about portable infrastructure, like a compact
greenhouse or shed that you could take with you when you go? Doesn't make much sense if you wouldn't have a use at your next base, but could show potential to viewers, and if they want it... great, pony up.