This park is great for finding solitude, and you do not need to get permits months in advance! Here are two trip reports I wrote that describe my backpacking trips in Henry Coe.
To Coit Lake - https://backpackersreview.wordpress.com/trip-reports/henry-coe-coit-lake/
To Mississippi Lake - https://backpackersreview.wordpress.com/trip-reports/henry-coe-mississippi-lake/