I'm not familiar with the Siletz (others on here are extremely familiar with it).
The problem you'll have with the Nestucca is low water. Probably 2 ways you can go -- use bigger gear, and fish at the mouth in Pacific City (park/boat ramp -- you won't be alone). Other options are to hit the area around the mouth of Three Rivers (in Hebo) with extremely light gear, since there should be a few summers there.
If you don't mind driving a little farther, the Trask would be a better bet. It'll all be fun, regardless.