We do this all the time. However, we have an extremely efficient coach, an enormous battery bank, and a 6,500 watt alternator. Even then, we can only run two air conditioners at a time.
We also have a generator, but we never run it when we drive, only while parked. If you are really serious about only ever parking where there is a power outlet, you might be able to get away without a generator, but that seems an ambitious goal -- power outlets can be mighty hard to come by in many parts of the country.
In any case, your 3,500 watt alternator is definitely not enough. That would run maybe one single air conditioner (about 1,700 watts while running; more to start), your fridge, and some miscellaneous stuff. Anything more than that, and you will be constantly depleting the batteries while you drive.
BTW, 8kW of inverters is impractical on a 12 volt coach. Some high-end 24-volt conversions have this much capacity (twin 4024s). We have a single 4kW unit, and it is more than capable of running the two air conditioners plus all the miscellaneous stuff, however, we use a DC fridge. The sheer size and number of cables you'd need to draw 8kW at 12 volts is daunting.
The only way to really know how much you will need and whether it is possible is to do the math. Don't forget to account for efficiency losses, which are in the 10%-15% range for DC-AC conversion, and in the 20% range for battery storage and retrieval. I suspect that if you plan carefully, you can get the total demand down into the 5kW range, and then you can use a pair of stacked 2,500-watt inverters. You'd still need to add about again as much alternator capacity as you already have; unfortunately, in a 12-volt application, that will mean a second alternator. They don't come much bigger than 3,600 watts.
HTH,
-Sean
http://OurOdyssey.BlogSpot.com
