I used 2 AWG welding cable from the combiner to the charge controller, and 2/0 AWG from the charge controller to the batteries. you should use 4/0 AWG on big systems. you can not go too big, you can go too small and loose watts.
The type of wire is not as important as size. You should be using a loom with any type wire you use that is exposed to the weather.
06 Hurricane 34FT WH W20 Chassis 8.1L 120K, Steersafe, Koni Shocks, DIY Trac Bar, Tri-Metric 2025RV Battery Monitor, 4-6V Batteries, Scan Gauge 2, Crossfires, 735W Solar Morningstar MPPT-60, KVH R5 In-Motion Sat, XM Radio, 07 Chevy Malibu Maxx Toad, Falcon 2, Brake Buddy, Escapee