How probable is it that truckers will get skin cancer?

Very likely: I have seen drivers have a higher rate of skin cancer on their left sides. Both the arm and face on the left side that get higher exposure to the sun have increased risk of skin cancer. This doesn't mean all truckers will get skin cancer but the side exposed to the sun is at higher risk.

Skin cancer : Since some uv light penetrates glass windows and obviously open windows, those including truckers are at a greater risk of developing skin cancer. The left side of the face and left arm being especially at risk on the driver's side. See a dermatologist for a skin cancer screening.