This is not really the forum for this kind of question. A better place to go would be an RV forum as this is more like what they do.
That said your worst case additional load with what you are talking about a little over 100 amps. That would be running your inverter at the point where it will trip off. Your stereo may have a 300 watt amp but average currents on modern car stereos are more like 30 watts. The guy you talked to was probably recommending the addition of a capacitor which will handle the peak loads to the amplifier.
I suspect you might need a larger alternator but it depends on what is already there. If you have a 140 amp alternator then you most likely don't need anything else. Ask this question on an RV forum.
That said your worst case additional load with what you are talking about a little over 100 amps. That would be running your inverter at the point where it will trip off. Your stereo may have a 300 watt amp but average currents on modern car stereos are more like 30 watts. The guy you talked to was probably recommending the addition of a capacitor which will handle the peak loads to the amplifier.
I suspect you might need a larger alternator but it depends on what is already there. If you have a 140 amp alternator then you most likely don't need anything else. Ask this question on an RV forum.
