The best place to drop your trailer is at your campsite and go exploring from there. I've camped and traveled up and down 101 and I can't really say any parking lot along the coast has a ton of extra spots for people to drop their trailers. If anything I've been warned of no over night parking in few and parking only while I'm shopping in their store. There are some dedicated public RV parking spots in areas, but it can be a challenge to get lucky and find one. Summer is prime season for the Oregon Coast, every spot matters to businesses.