Jono,
I put hubcaps on my first A Model IV. I need an oath of secrecy before I tell the next part. Thanks! My wife is a flight attendant and I occasionally take advantage of her time away to use her things for my projects. The lid of her favorite frying pan had the perfect contour for laying up a couple of convex shapes that I trimmed for the covers themselves. To attach them to the wheel, I found d some aluminum flanges - similar to the ones that secure the large hose under the header tank to the belly fabric, but larger - that I glued to the wheel hub after attaching three anchor nuts. I used carbon fiber tubes as spacers between the hubcap and the flange.
I no longer have the original airplane but do still have the hubcaps. I put many hours on the airplane with the hubs. The only issue was the flanges made checking air pressure and adding air a little more of a challenge.