Ant gel or Raid double-action ant bait. Yes, they use insecticides but you're not blindly spraying it in the car. The ants eat it, take it back to their nest and it wipes out the colony via communal feeding. In the case of the professional stuff(Bayer Maxforce gel or Syngenta Advion), I've actually seen ants die on the way back to the colony.
Gel/bait uses albamectin, dinetofuran or indoxacarb - which work at a lower rate of AI and are toxic to ants/roaches but have almost little effect on humans. I know the local transit agencies use Maxforce or Advion ant/roach gel to keep them free of ants and roaches.