I can't think of any areas of 101 that your coach can't handle, and I've traveled it numerous times as a native Oregonian. But some smaller side shoots and waysides can be too small for you, so set up camp and do any gunkholing/curiosity-satisfying in your toad. I have to agree with Butch about those areas he mentioned on the south coast, as the highway does a bit of twisting to get around the bluffs and dark coastal woods, with a hill or two for good measure. The copilot may enjoy a great view while the pilot tries to concentrate on where they're going, but it's not bad at all as long as you keep your speed close to the posted for curves. And those sections involve only a few miles.
Most Oregon State Parks on the coast are quiet and a great value with access to beaches and towns nearby. Park for a couple days and venture about in your truck. After Labor Day, the crowds subside as the kids go back to school, and it's one of our favorite times to head that way, though we enjoy the winter on the coast also - choice camping spots, vacant beaches, wild storms outside while tucked comfortably in our Beaver coach followed the next day by great finds on the beach, whales migrating south, cheaper rates, etc.
A few places to enjoy:
Fort Stevens State Park with a toad trip to Lewis & Clark's Ft. Clatsop;
The promenade at Seaside;
Cannon Beach;
The great Tillamook County Park at Barview, north side of Tillamook Bay;
The Tillamook air museum in the blimp hangar south of Tillamook (there is a campground at the associated airport, or toad from Barview), and tour one or both of the two Tillamook cheese factories north of Tillamook;
Explore the large towns of Lincoln City and Newport, with a check of Depoe Bay and Otter Rock inbetween;
Visit the Aquarium at Newport, and the Mark O. Hatfield Marine Science Center on Yaquina Bay (Senator Hatfield just passed away this evening at 89) - you can camp at Beverly Beach SP, South Beach SP, or stay at the large open RV Park at the Marina on the south end of the Yaquina Bay Bridge;
Spend a couple of days enjoying Florence (Jesse M. Honeyman SP) and the Oregon Dunes;
Definitely enjoy the Winchester Bay Marina and RV Park, the town of Reedsport nearby, and more Dunes;
Tool around the lakes and dunes around Lakeside after setting up camp at Osprey Point RV Resort;
Rag on some one-armed bandits and enjoy a meal at the Casino and RV Park in North Bend/Coos Bay;
and don't pass up our favorite town on the coast, Bandon, with a night or two at Bullard's Beach SP or one of numerous private parks - check out the quaint museum downtown and Face Rock south of town, or if you're a wealthy golfer, take a round at one of the world class courses nearby, and pick up a souvenir at a nearby Myrtlewood "factory" or store;
Camp at Port Orford and toad over to the nearby lighthouse for a tour, or the historic farmhouse/museum a hop-skip away, followed by a hike down to the mouth of the Sixes River, with the river and beach all to yourself (I love the place), and next day pick up on the ambience of Port Orford and historic Battle Rock;
Head for Gold Beach's Oceanside RV Park or one of several others, and register at nearby Jerry's Rogue River Jet Boats for the exhilirating trip up the creek to Agness for lunch, or hire a guide for some Fall Chinook fishing on the Rogue, or drive the coach up Jerry's Flat Rd. to the RV Park at Agness, where the Illinois River comes into the Rogue;
Stay at Harris Beach SP and explore Brookings, a place many elect to retire to (Oregon's own Florida) and you'll see why;
From there enjoy Crescent City, the mouth of the Klamath River, and the Redwoods beyond, perhaps even finding gold under the Gold Bluffs like I did.
:oWhew...Well, you asked
-Joel and Lee