Cascades, Crater Lake, Redwood National Park

Just FYI - if you do decide to stay at Tumalo, be aware there are VERY few sites capable of holding that 45' trailer, if any at all. We stayed there last fall and most sites we couldn't even have gotten our 27-footer into. Nice park otherwise though.

Seems a lot of the SPs on the Oregon side along the Columbia River are right next to the interstate, so be prepared for road noise.

We stayed at the Columbia Riverfront RV Park in Woodland WA to explore the Columbia River Gorge. A bit tight but doable. They really enforce the rules!! Check out photos on: http://www.columbiariverfrontrvpark.com/ We had a pull in river view site. Be sure to make reservations and specify rig lengths. We got the last 2 sites and couldn't be next to each other as they were booked.
For Crater Lake, we stayed at Seven Feathers Casino RV Park in Canyonville OR right off I-5 and drove (about an hour) to Crater Lake. Beautiful drive! Seven Feathers is also a fuel stop with cheapest fuel in the area. Very nice travel center. Be sure to visit Tillamook Cheese and Ice Cream shop in Tillamook OR, and have lunch there!! Or skip lunch and just eat the ice cream!
For Redwoods, in Crescent City, stay at the KOA and drive (in your tow vehicle) the Howland Hills scenic road into the Redwood forest. Awesome!! you can google it for directions. Then, move down to Redcrest CA to Ancient Redwoods RV Park on Avenue of the Giants. You can walk out of the RV park into the Redwood trees!! Don't miss either one.
Been twice and we can't wait to go back!!

To add to what Don and rbtglove noted in the Florence area is Jesse B Honeyman State Park and Harbor Vista a Lane County Park. Both take reservations and have some FHU sites. Our 5th wheel is 33' and not a problem in either park. Harbor Vista is smaller park in the number of sites and still has sites to take your friends 45' unit. Most are not FHU, but I believe they have 3-4, and do have a dump station on site. It's one of our favorites with how private most of the sits are. The Central Oregon coast is where we spend a lot of time as is Central Oregon. Some nice places to eat in Florence in the Old Town section. PM me if you would like more details and enjoy being in Oregon!

In the Gorge we use Ainsworth State Park near Troutdale, does have FHUs and very scenic. Some large pull thrus. Near Falls, but a no reservation campground so get in early. Also like Memaloose State park near the Dalles, has a great location on the river some FHUs and will take reservations.

Well for starters Columbia river rv in Troutdale,OR is full hookup on the Sandy river close to the gorge and Portland. From there I would opt for either Tumalo or LaPine state parks. Lots of things to see and do. Next would be Diamond Lake resort. Close to Crater Lake. Then maybe Valley of the Rogue state park. Historic Jacksonville is a worth while ghost town. From there north to Grants Pass and down to the coast on 199 I think it is. Dont forget Oregon Caves N.M. you come out on the coast right at the Redwoods.

From Portland area Mt St. Helens is a nice day trip. Same for the gorge.
As an alternative you can head farther north on I5 and cut over to the coast just south of Eugene to Reedsport. Winchester bay RV is right on the bay with great views and a chance to visit the Oregon Dunes. South on US101 there are lots of places to see and do. Any of the Oregon state parks will be greal, but you will want reservations.

PM me if you want more information