just outside Florence
For all who might be interested we found a nice spot on the central Oregon coast just last fall. Just South of Florence turn West on South Jetty Rd.
There's a sign marking it: "South Jetty Dunes and Beach". There was also a small RV dealer/store at that intersection. This road provides access to the North end of the Dunes recreational area, but if you pass by all that and just keep following the road it turns North along the Siuslaw river and continues to the South jetty.
At the end of the paved section the federal jurisdiction ends and you are actually on county park property. A very short drive over gravel takes you to a fairly large parking area that sees regular use by boondocker types. The road doesn't look all that great but I wouldn't hesitate to take my 36' class A over it, just don't try to go any further than the wide gravel parking area - it's all sand after that.
Usually not more than one or two at a time there and generally not for more than a few days. Like many similar spots, technically we're not supposed to camp there but when cops do stop by they mostly want to see that everything is safe and don't make a habit of hassling campers.
It's really a nice spot. If you chicken out or just decide you want hookups Harbor Vista RV park is directly across the river (and about 10 miles away by road) and it's one of the nicest county RV parks we've seen.