I’m going to speak up for a Fastrac and demount system. 2500l on the deck and another 1500l on the front if you want.
Plus the ability to tow a huge bowser on the back if needed.
Speed on the road and just about every convenience of a SP with so many more advantages and a tractor to boot.
What more do you want?
A very valuable suggestion. I had a demo of a 4220, and aside from being impressed with the machine and amazed by the comfort, I must admit my immediate thought was how good it would be with a landquip demount on it. My ignorance prevails as regards to how difficult a demount is to attach, but certainly food for thought. Are they noticeably higher than a SP for road transport?