Alabama's laws are very very unclear and they have left enough room for anyone to argue and win a helmet ticket. If I'm stopped and they say anything I simply go thru my "side car" defence...
Basically in Alabama a side car is considered a enclosed vehicle and no helmet is required. When you ask why they don't require a helmet the answer is.... "because you can not put your feet on the pavement when stopped". And thanks to that definition I dont have to wear one in the slingshot.
Remember to look over all the little loopholes in your state's law book. And make sure they havent added some new laws for other three wheel vehicles that may help you out. They may not in the first place you look for relevant laws. You may have to dig deeper to find the new additions. And mainly ...... print the most pertinent pages and highlight the lines that you want to get to fast. The side of the road is not a courtroom. And you need to simplify your reasoning quick and without a hickup of doubt in your voice. If they still want to write the ticket just let them and go to court and show them your papers and explain your side. No big deal. It's not a ticket that goes againt your points on your license. It's just a fine.
I wear my harnesses when I'm in my sling. I keep them very snug and I wear shatterproof glasses. I do keep a "skid lid" helmet tucked under the edge of the passenger seat. Because I might meet the one officer that wont let me leave the scene without it on. And I don't need that much drama in my life.
But as far as using a helmet...... not when I'm just driving. I just use it when I'm at the race track. And to add to that.... I now have a full fire suit and neck brace and gloves and boots that I have to wear at the track. The East Coast Timing Association rules are a bit tougher for the 1 mile and the Land Speed Record events. You will comply or they wont pass you at inspection.