We just bought a 2019 Transit 350 passenger van and plan to convert it into a camper van. The installer I'm talking to says I need a Parallex 45 amp converter with 2 AGM batteries. After researching batteries, it seems to me that I'd be better off with one lithium battery rather than 2 AGM. My installer was totally dismissive of the idea. I guess he wants to do what he wants to do! We have only talked, he hasn't started anything yet and has not quoted a price. Should I follow his advice or try to find someone else?