Another suggestion - I see you're from Alabama. You could reverse that trip by going up through Oregon on Hwy 97 at Klamath Falls. Stay at Collier Memorial State Park - great for a 40' motorhome - and drive your toad over to Crater Lake and see as much as you can. The road around the lake will not be fully open but will be to the visitor center with views of the lake and would be worth the short side trip. It would be a shame to pass it up completely if that's what you planned to do originally.
Then continue north on 97 through Bend and pick up 26 at Madras taking you into Portland. This is a very scenic drive and again, good for a 40' MH. Cross over to the coast via Oregon Hwy 30 or Hwy 4 at Kelso, Washington and take either one over to Astoria for your coastline trip south on 101. Crossing the Astoria bridge from Washington is awesome!
We, too, would recommend heading south along the coast - especially with a big rig. It's so much easier and safer to use the scenic turnouts on the right-hand side. We've done this trip often with our 40' motorhome as we gave the lighthouse tours at Heceta Head at Florence. There are so many neat areas to stay overnight and to check out the areas fully. We have made many stops at the state parks without having reservations in May.
Then enter California. For the redwoods we loved our stop at Redcrest at Ancient Redwoods RV. It's excellent for big rigs and it's right in the midst of the giants. Nearby are so many gorgeous short trails weaving in and out the redwoods. Then continue on 101 down to the San Francisco area and wherever you're heading next.
Have a great trip!