I wouldn't use anything but PEX, it's really easy to work with and made to never leak. The slip on "Sharkbite" connectors work great, just make sure to insert the pipe fully. Cover as much of the pipe as you can with foam pipe insulation to prevent buzzing against the vehicle body, and to protect from freezing.
I would recommend an accumulator if you are using a fixed-speed on-demand pump to reduce cycling. If you have the $$$ use a variable speed pump.
2015 T250 cargo, 148" WB, Medium Roof, 3.7L V6