Expedition tank?

I usually carry a Red 10 litre "Squat Tank" which i chain down in the rear compartment of the car. That gives me a bit over 100 kilometres range and since it weighs only 10 kgs is easy to hold while emptying into the Jimny. Yep, I'm getting old. With the drums you see on the outside of cars in Oz, only the Green ones may carry water. The Yellow Ones (Diesel) and the Red ones (Petrol) are required to be carried internally in case of collision. Insurance is void in all States and Territories if fuel is carried on the outside of vehicles in Oz. Despite this you often see fuel carried externally. Cops love them, an easy revenue earner.

If you don't want to lift fuel have you considered using a 25 litre outboard motor tank? That would give you heaps of range, is portable and could be manually or electrically pumped via a fuel pump into cars tank whenever required.
They come in all shapes and sizes.

If you could re-route the exhaust to go straight out the LHS with a smaller back box then you could free up 25-30 litres of space behind the axle. Should be a good local vehicle engineer somewhere that could cobble something up for you that integrates seamlessly with filling and emptying the original tank because the levels would all be similar. Otherwise it's a can in the boot. Assuming you have nobody in the back, a 5l can behind either front seat works easily enough, but obviously filling and emptying is a faff.

That is essentially what I was thinking of doing.

What's under the seats? quite a bit of room there!

I've actually given some thought to splitting the upper and lower halves of the tank and putting a 2" spacer in there.......also thought of making a new tank in Alloy and having a side exit exhaust.......so many projects!!

Well, when I was under there last week cleaning i gave the tank a course of looking at. It only drops on one side of the rear propshaft and then short of the bottom of the chassis rails. With a second cross pump like a subaru to lift from the opposite side a minimum of 10 to 15 litres could easily be gained, more if both sides come flush to the rails, suitable guard notwithstanding. Need a man who can tig weld aluminium neatly.

You probably need someone who just laid 2K on a magnetic folder,edge setter and access to a bead-roller too?

Know anyone?