We've had two experiences like your drive to Alaska. We drove there and across Labrador when it was a 1000 mile dirt road. On the road to Alaska we had our windshield hit three times by stones, each hit was caused by oncoming traffic and all 3 hits on the driver's side. We were driving our motor home towing our Honda. The motor home's tires
are pretty far from the tow vehicle. We had large mud flaps and a barrier along the back of the motor home, sort of like your truck flaps and had no tow vehicle hits.
We did put clear mylar tape across the front of our headlights as well people often put clear mylar tape on the lower part of their windshield, the part you're not looking through.
On our trip to Labrador we put blue insulation foam on the front of our gray tank and on the front edge of our fuel tank to protect from rocks, These pieces were generally peppered with holes and no damage to the tanks. (By the way a bar of soap can fill a small hole in a gas tank).
We had an aluminum faced trailer going across Labrador, Every front facing surface was sand blasted on the Labrador road and the paint
worn off the front of the trailers in the area immediately behind the wheels. It seems the flaps almost needed to go to the ground to stop this peppering. Labrador road is mostly paved now and the roads in Alaska are mostly paved, it's in the construction areas where you need to be careful and shockingly to us it was not the guy in front of us but the guy coming towards us.
In Labrador for oncoming traffic we would normally pull way to the right and let them fly on their way. We would only see about 4 cars a day coming towards us and another 4 pass us in our lane, they all drove a lot faster than us.
We went to Alaska in 2003 and the traffic once you get north is relatively light
and virtually no 18 wheelers.