Have made that trip a couple of times and it's a hoot. Can't comment directly on a oversize DP, but we never had any issues. There's no pass to climb, you bypass the Siskous, so that's a plus. Redwoods are fantastic. Oregon coast too but lots of stop and go thru little towns. Some amazing places to stop and visit. Off season even better. Did it one Christmas holiday and it poured rain the whole time in Redwoods and we had a ball, never saw another soul.
Humbolt is pretty long and twisty. Cut over from before Sacramento, take the coast. Don't drive Big Sur, too tough in the big rig, 101 is fine all the way from LA. But from SF north should be good.