To Prep "Thataway" for a road trip on the interstate, we put a coat of heavy wax-not well buffed out over the bottom and exposed frontal parts of the hull. We also put a heavy coat of "RainX" on the forward glass.
We had done the AlCan with an RV--and our decision was not to tow a car, but to carry a motorbike on a rear carrier. I would want a mesh screen on the front of the trailer. I have seen the "shade" cloth obtained at Home Depot, electrical tied to PVC pipe to act as spreaders to keep gravel off the front of the bow, from the road. I have seen folks shrink wrap boats--but then dirt gets under the shrink wrap--and abrasion occurs. I have also seen cardboard cut to the size of the windows, and duct taped in place.
We took Frequent Sea over the road to Prince Rupert and only used a heavy coat of wax--no evidence of damage. But if we had gone on gravel roads, I would have used the mesh to protect from gravel thrown up by the rear truck tires.