For pure scenic traveling, it’s hard to beat the Oregon Coast where you will find one of the world’s greatest stretches of scenic byway (363 miles of Coast Highway/US 101) that leads to many great destinations. Although Highway 101 is primarily two lanes and winding in portions, it is probably the most popular byway for RVers in Oregon. With numerous Oregon State Parks campgrounds, private RV parks and RV parking at many of the coast’s top attractions and natural areas.
If you have the time, you could travel all the way to Brookings, then begin your return by following (US 199/Redwood Highway) back to I-5. This would enable you to choose from many other options as you travel north including the great town of Ashland, famous for live theater and Shakespearean Festival; several portions of Oregon wine country, perhaps make a side trip east to Crater Lake, see historic covered bridges in the Cottage Grove area and visit beautiful waterfalls at Silver Falls State Park. This route would just leave you with a few great areas in Central Oregon (Bend) and Eastern Oregon to check off your list of great scenic destinations in the state.
My specific recommendations would certainly vary depending on the time of year you are traveling, your own interests and how much time you have, but I hope this gives you some ideas.