I must preface this post and say that I am not sure if this is actually a legal place to park. We cannot locate the original post that led us there in the first place so please take this with a grain of salt.
Our BEST ADVICE for traveling the Oregon Coast and boondocking:
It was difficult to find places to stay along the coast for free BUT if you can manage to find places to lot dock and scoot in the morning, there are TONS of cool places you can park your rig in parking lots right next to the water in the State Recreational areas that are open for day use. A lot of them even have free water, dump stations, trash cans, and bathhouses should you need them. So if you can find a place to crash for the night, you can keep moving on the next day and mosey up the coast.
Minor Park Rd in Waldport 44.435412, -124.074752
This particular site is just a simple parking lot next to a bridge. There were no "no parking" signs at the time and it was suggested on freecampsites but is now nowhere to be found. It is right outside of a KOA so I'm sure they are not happy about people parking over night for free right outside their campground.