our R51 pathfinder (80l) could only get a bigger tank if we removed the spare wheel from underneath, as we have lived and worked remote we already had a 2nd spare on swing way wheel carrier on the back, and didn't want to only have one. So extra fuel was always in Jerrys, much easier now we can carry them on the Camper draw bar. If it could be done with out loosing anything (I think it can be done on the DMAX) I think its a good thing. The DMAX at work has a 140ish l tank, fuel gague work ok, looks full for a bit longer, and goes down a bit quick from half way, but if you know how much you put in and how far you should get its fine. Personally I hate stopping for fuel, Ive always kept this in mind when looking at motorbikes which often have small ranges.
I think you need to look at where you will be traveling to work out if it is cost effective. Across the Tanami it is along way in between drinks, same with Simpson and plenty of more remote 4wd destinations. Otherwise you can normally find some where to fill up within a shorter range (350km), just paying a bit more. Some people think its a good excuse to stop and stretch legs, find a loo and take some photos.
I would prefer to limit my handling of fuel and keep away from jerrys as much as possible, but its a cheap option if you only need to do it occasionally.