The beetle cases were a magnesium alloy while the Vanagon cases are Aluminum.
 So you don't have the magnesium problem to worry about here.  I would carry
a nice CO2 bottle to put out engine fires with.  These are great on fires and
when you get done they don't mess up the engine or engine compartment like
the chemical exstinguishers do (I sprayed one of these on my Rabbit pickup
motor when I thought it was on fire and it ate all the paint off the motor!)
Water is not a good idea because if it is a fuel fire or oil then you are
just splashing the oil around which actually makes it burn more quickly
(hence the great balls-o-fire action).
Hopefully you will never have to use this info.
Ken Wilford
Van-Again
John 3:16
PS A good chemical extinguisher is better than nothing!