In the previous post, I wrote about the inherent inefficiency of automotive alternators as a continuous power source, specifically for powering an air conditioner. In response, I was asked what makes them so inefficient. The following is my (somewhat educated) opinion.
The main problem is that automotive alternators are designed to produce enough voltage to maintain the battery, even at an idle speed. This means that at any speed above idle, they are wasting much of their capability. They can be rewound for efficiency and converted to a permanent-magnet configuration, and there are sellers on Ebay who sell just such an alternator, primarily for building your own wind generator.
This would actually be a pretty good solution. What you would do is run this as a second alternator, dedicated to the "house" battery bank. You would need to find a seller who winds his own stators, and consult with him about what you want to do. The alternator would need to supply about 50 amps at the battery bank terminals, at your normal cruise speed. You would then need to buy (or build; they're not that complicated for an electronics hobbyist) and install a diversion regulator which dumps excess power into a load anytime the battery bank exceeds 13.8 volts (for a 12 volt bank), such as when the air conditioner cycles off or is not being used. This regulator is necessary because such a modified alternator outputs unregulated power. If you are not going to be using the A/C (such as cool weather), just remove the belt from this alternator. The load you dump into can be an electric water heater. Sounds complicated, but it is probably the best alternative to having a separate, mounted generator.
Personally, I would go with the mounted generator (preferably diesel) and a good inverter with a built-in high rate battery charger and transfer relay (which transfers the load automatically from the inverter to the genny anytime it is running), because you can use it when you are parked, as well.