It would be cheaper to get 2*150A batteries instead of 3*100A batteries, it would also be easier to set up and requires less cabling since he is going to need to wire them in parallel, although I think it would be wise to run them in series and get a 24V inverter instead of the 12V, a 24V system has a few advantages over 12V system, with the exception that you can't expand your batteries with 1 battery at the time, you will always need to do them in twos.