Hill Country SNA is an option, as well -- there are a couple different primitive campsite areas that require a hike-in and you can take however roundabout a route you want to get to them if the shortest distance is too non-backpacking like (eg. makes you feel like you're just hiking with too much stuff on your back.
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I haven't backpacked at HCSNA yet, but I've hiked and camped there many times.