The first picture is worth a kilo-word.
aerohead covered it. If you want ideas search on 'time attack' and look at their body add-ons. You only difference will be the lack of flare to cover expendable rubber.
I have a Dish antenna that is a 36" oval I was going to use as a female mold for fiberglass bubble skirts. But I don't like fiberglass. Thanks for not using Coroplast. It's Okay for mocking up, but my favorite would be Polymetal:
It can be worked with hand tools. It can be rolled, braked and sheared (all three shown) by hand with an 18" lever arm. One disclaimer, if fire penetrates the aluminum skin it turns into a little piece of Grenfell Tower.
While you're still at the design phase is when to think about the skirts' proximity to the belly pan, wheel spats and rear diffuser. Even if you don't do it all at once, with a plan, it can all come together.
