I have an IOTA 90Amp converter, just plug it into a generator or mains and you are charging at 90amps. Its only about 4x6x10 inches, about the size of an inverter and fits under the floor in the camper. Its also a perfectly clean power supply as well as a charger so its safe to run while you are using power. The gas powered alternator would have the same benefit which can't be said for all battery chargers. A 1.8kw Brigs engine probably takes more gas than the E2000 and makes a whole lot more noise. I think the converter is the best of all solutions as you can charge silently if mains power happens to be available, you can use any generator of your choosing, its also one less thing to carry.
A better way to carry a spare alternator would be to charge the aux battery with a second identical alternator and do away with the isolator, replace it with an jump switch so you can join the battery banks should either of the alternators fail. No tools required, just flick a switch and continue driving. You might have to disconnect the power connector to the broken alternator if its shorting or making dirty power.
You can also use the switch to join the batteries and alternators if you need lots of power for winching or fast charging (useful when idling the engine or driving a short distance). When winching, with 2x130amps from the alternators you'd be pulling really hard on the winch before you even touch the batteries.
This is how my mog is set up, it uses a solenoid for the transfer. I have never had to use it because both alternators work but its good to know its there.
Rob
