A loincloth would do. There are no clothing rules. Most shooters wear long-billed hats. You'll get one very soon either from the club, a new friend, or manufacturer who sponsors trap shooting. Generally, just wear what you want.
Shorts are fine.
Bring sunglasses with you. Dress for the weather. You can make money in trap shooting and many shooters do to at least help pay expenses. Now you know why the rich people wanted to keep this sport all to themselves. That's right, you can.