Perhaps a separate sufficiently sized alternator could be installed on
the left side of the engine where the A/C compressor is in A/C equipped
Vanagons. 120 Amp alternators are becoming standard on new cars, even
VWs. They do use a much wider type of belt so the Vanagon crank pulley
may not do the job. Mount one of these for only the inverter and a large
deep cycle battery (leaving the stock vehicle electrical system alone).
No good when the engine isn't running but run it off shore power then.
How much is a 1500 watt inverter and will it really run a small A/C unit
during compressor motor startup? How about the Vanagon engine? It may
stall at idle with the A/C running or at least when the compressor motor
starts up or cycles.

Mark