To face a **strong gust of wind** when transporting a trailer, it is advisable for the towing vehicle to have a **wind deflector**. This accessory, also known as a deflector, is installed on the vehicle to **divert the air** and prevent it from entering the interior. This is especially useful in strong wind conditions, as it helps to **reduce air resistance**, improving vehicle stability and decreasing fuel consumption.

In contrast, other elements like the **roof rack** can increase air resistance, which is not recommended in strong wind situations. Additionally, carrying **two spare wheels** has no direct relation to improving stability or wind resistance. Therefore, the wind deflector is the most suitable option for these conditions.