As you know The Sequoias and the Redwoods are far apart,close to 500 miles. The Redwoods are on the California and Oregon Coast while the Sequoias are on the western slopes of the Sierra Nevada range in California,at 5000 to 8000 ft.
If you are going to see both it will be a really nice trip. Mid September is getting close to the end of summer for the school kids,but to be safe I would get reservations.
In the Redwoods
This Place is Big Rig Friendly as are the people that run it,and with a Toad a great base to explore the
Avenue Of GiantsHave fun and enjoy our Great State.