"as close to the batteries as possible". Really? I've seen many OEM inverter/charger installation, with 15' or more of properly sized cable. I just did a little wiring repair on a Monaco Windsor that had a 3000 watt inverter/charger with over 12' of 4/0 cable. Country Coach use to put the inverter/charger behind the front axle and the batteries back by the diesel engine. That could be 30' or more of cable, using the frame as ground. Do the math and put your inverter where you need to, with the proper sized wiring.
Richard