I used barbed fittings and clear vinyl reinforced hose in my conversion. The vinyl adds a little insulation to help prevent freezing, it is a little flexible and acts like an expansion tank in reducing cycling of the pump and I found it to be more flexible than PVC or PEX so I used fewer connectors. You can also see what is in the hose which is kind of handy for the grey and black tanks.
You should think about weight distribution. I ended up moving my tanks to the front to offset the weight of bikes and gear in the back. Trying to get almost equal weight on all tires with slightly more in the back.