Best way to implement BLIS in a car with Arduino?

Hello,

I want to implement BLIS (blind spot system or something like that) in my car with an Arduino. I have been considering different ideas, but I concluded that using ultrasonic sensors would be the best idea bearing in mind price/performance/size. The problem I´ve just realized is that ultrasonic sensors are (obviously) affected by wind. And there is gona be a lot of wind when using BLIS (it activates from 40kph-60kph to 130kph-140kph according to the car), so when the Arduino tries to measure it, it won´t read anything.

I know that I can use a camera with Raspberry Pi and a special software or a laser rangefinder, but these aren´t cheap and accesible in Argentina.

The other problem, and most important, is that I need to "hack" some ultrasonic sensors from parking sensors because they are waterproof.

Thank you.

Sorry for my bad English.

Nicolas.