The Subaru charging system is adequate for a stock Subaru but if you plan to add all the extra loads on the electrical system that we do in our adventure vehicles it's probably a good idea to upgrade the charging system supply cables, the battery to chassis ground, and the ground from the engine to the chassis ("the big three"). This kit uses super high quality 6 AWG wire from the top alternator post to the 12v+ lug on the back of the starter. It uses a new alternator control plug and wiring, and is protected with high quality braided split loom and heat shrink. The Vanagon specific kit also has an 8 AWG wire from the starter to the engine bay black box paired with an extended alternator charge lamp wire and connector, along with a new "Black Box" grommet. Unfortunately I haven't found a great supplier for the alternator 12v+ boot so you'll need to use your existing one for the time being.

DIY Upgrade: Go to the auto parts store and buy a battery cable long enough to go from your alternator top lug directly to the battery in a bus, go to the 12v+ lug on the starter for Vanagons and other aircooled VW's - basically just copy the above design using your alternator control plug wiring.