Do you have a quality set of jumper cables?
Many vehicles idle speed Alternator amperage output is pathetic but some are pretty good. If it can do 30+ amps and maintain 14.4+ volts over some 4 awg cabling then hooking battery to battery with engine running will be more effective than using an inverter to power a 30 amp smart charger.
Also when batteries are cycled heavily without an intervening full recharge, one cannot really compare charge times requirements as to how depleted they were to begin with.
Even less trustworthy is when an Automatic charger flashes the green full charge indicator light. They all stop applying absorption voltages and revert to float way too early on a heavily cycled battery, and when fed by a MSW inverter, I bet this is even more a case of wildly premature efloatulation. Scumbag 'smart' charger liars.... grumble grumble
In your case, assuming the house battery bank is well grounded to the frame, I'd order a 2awg cable, or thicker, from Genuinedealz with ring terminals on one end and an alligator clamp on the other, and hook one to the house battery and the other directly to alternator (+) output and hold the engine at 1000 rpm for an hour, when needed, and not worry about getting the batteries past 80% charged. Bypass that too thin original alternator to engine battery circuit and more amps will flow, and the voltage regulator will likely allow higher voltages, and thus higher amperages, for longer.
But if the VR only allows or reverts prematurely to 13.7v, forget this plan.
