So I bought a 2010 Alpine Explorer on clearance and man does it rock. Just enough space to cram in all my gear for an overnight trip but small enough to use for day hikes. The only problem is the 3L reservoir would only keep me hydrated for one day since I drink a lot of water.

Today a lightbulb came on and I slipped my SixBac 6lt reservoir into the back and voila. It fit perfectly. Now I've got 6L of water.