I think if you cover it with thatch it would make a great duck blind! ;-) ... sry ... just having fun...
I do like the idea... Don't listen to the negative a$$-essments. Prototypes are generally rudimentary anyhow. After all you want to know what works before you go all out on the idea.
I think an aluminum tubular frame bent & welded and then painted to match would look nice. I wouldn't recommend powder coating for this as it can be difficult to match and maintain. I've had bad experiences with this and prefer vehicle color matched paint or just black so I can easily fix it. Also I think metal swivel rollers on the trailing edge and a vertical pivot point at the hitch with a elevation stop welded on would be a good idea. This would avoid any scraping.
I've always liked the idea of a low profile, lightweight, closeable & lockable box carrier on the hitch. I know a simple one would be easy enough... though I think a molded or shaped one would look better and maybe even be aerodynamically functional, offering less drag than a simple box. I think a box that has custom fitted suit cases would be awesome! Think about it. The biggest problem with any carrier is the shape & size of the darn thing to get travel bags inside it. Your almost stuck with duffel bags and they can be difficult to fit right. Personally I think custom hard suitcases that fit with wheels for airline travel when needed is a great idea.
Another idea I had is simple square aluminum boxes about the size of a carry on that fit a rack and twist buckle together at the sides to form an interlocked box to the rack size. I've always been the pack mule in the family and it's a pain in the butt to fit assorted luggage.