I agree the Re-Gen creates lots of heat.
You have 2 different types of Overheat.
First step is to find out what’s over heating.
Is it the Motor or is it the Controller. Example No use adding vents to the hood if it’s the controller that is overheating.
#1 the most common is -41 “Controller Motor Over Heat” if the controller overheats it puts your car in limp mode.
You can add a heat sink and fan to the controller to keep it cool. This Is talked about in a thread here on this Fourm called “Cool Air Kit”. Gem Cool Air Kit
The #2 is actual “The motor gets HOT and overheat’s”
This is from hills and heavy load and slow speeds. You can add vents to the hood and scoops to the sides to draw in cool fresh air.