Once you cross into WA it is mostly 2 lanes, one in each direction with pullouts for slow moving vehicles. It does have some elevation at times but nothing like a mountain pass. It is also somewhat winding as it generally follows the coastline. All this adds up to an amazingly beautiful drive. My advice is to take Highway 1 from Raymond to Westport which will get you closer to the ocean. North of Hoquim your only choice is 101. You shouldn't have any issues towing a trailer other than cars wanting to pass you. The only issue you may face is finding a campground as this route is very popular in the summer.