I would suggest just about any of the Oregon State Parks. Your 30' RV would fit just fine. All three of these have nice beach access and are in areas with lots to do. I would also suggest you choose 3 areas of the coast:
North - Fort Stevens by Astoria
Mid - Carl Washburn by Florence
South - Bullard Beach, Bandon
Have a good trip. It won't be crowded at all.
Full-Timed for 16 Years
.... Back in S&B Again
Traveled 8 yr in a 40' 2004 Newmar Dutch Star Motorhome
& 8 yr in a 33' Travel Supreme 5th Wheel