I made this tutorial years ago for improving onboard audio in track day/race recordings. I've installed essentially the same gear in my FE. In there I have had to worry about overheating issues and water intrusion, but for the most part the concept is the same for a tin top as it is for open wheel. Get the microphone(s) out of the airflow and closer to the stuff that sounds cool. My S4's turbos, diverter valves and wastegates always made for lively engine audio. That said, mixing in the camera mics for the wind effect as well as noises from the other cars will help provide some stereo too as most likely you'll have mono recordings.