Depends, side by side or end to end. Basically fill into first tank, cross over to second tank with the vent alarm and gauge in the second tank. 1/2" cross over on the bottom using heat melt fuse valves on each tank. 1 filter off the bottom cross over with supply line going to the appliance.
A good HVAC tech knows how, an educated HVAC tech knows why!
2 2" fills, 2 2" vents, no copper. I don't like/recommend piping them in series, even though it's not against code in most places. If your going with Roth tanks or equivalent, they make manifold piping for supply, vent, and oil lines.