Chuck is right about time.
When I think of fern canyon, It is North of Eureka. Camp on the beach. It is called "Gold Bluffs Beach". Hidden treasure. I use it. on your particular route I would camp about 14 miles North of Westport. just past the last "campground" about 200 yards on the opposite side of the road is my secrete spot. don't pull in very far off the road maybe sixty feet, under and behind first set of trees. just before 101 leaves the coast. this is about 3 to 8 miles before you pull off on Usal. I camp there often. then You will be taking the "Lost Coast" and spend a good portion of the day making it to Brookings. I have another trials event that weekend or I would go with you.