Yeah that’s going to add some weight! I think most of the time I’ll keep 5-10 gallons in it, which I hear is not noticeable. I think my next engine will be Diesel!
Diesel can be a real problem if you plan to leave North America or Western Europe. Newer diesels require clean ultra low sulfur diesel, because of the particulate filter (DPF). One tank of high sulfur diesel will very quickly clog the DPF leading to extremely expensive repairs, and ULSD isn't everywhere in the world yet. If it is there is it fresh and clean after being transferred from container to container, any problems in the fuel will lead to problems in the DPF. A diesel can be reliable in the third world if you do a DPF delete or it never had one in the first place.
Newer diesels really need long run times for the DPF to work properly, back and forth in town to the grocery store doesn't get it hot enough. It is important not to idle a diesel, it was never good to idle a diesel because there a direct injection engine. I think in the early days idling diesels was a thing because they were hard to start, so you didn't shut it down until the work was done. Spraying either in the intake and hoping you can get it to start, but that didn't mean that idling was good for them. The injectors can't spray a nice cone when idling and this leads to all sorts of issues inside of the piston as well as premature injector wear. Never use either in a modern diesel!
In the third wold scooters are everywhere so you can find decent 85 - 87 octane gasoline just about everywhere. with a possible exception of Australia and some extremely remote portions of Africa. Much of the stability problems in gasoline in the states has to do with the fact that much of it is E-10. E10 gasoline contains 10% ethanol, and that is water miscible. When water gets into E10 gasoline it becomes unstable as the ethanol becomes heavier than the gasoline and drops to the bottom of the tank. and your engine sucks in the water/ehtanol mixture clogging the filter and filing the bowl if you are still using a carb. Water enters the fuel condensing out of the air above the fuel in the tank or from leaks in the tank or lines at the station. The remaining gasoline on top of the water will have a low octane rating, because ethanol is used to boost the octane of the gasoline. There is water finding past you can buy to test for water in gasoline, turns florescent green in the presance of water. Gasoline that doesn't have ethanol in it is immiscible, the water remains separate from the fuel and is easily removed. Worry less about brand of fuel and more about how often the fuel is delivered, try to go to stations with a high turn over of fuel. I deliver fuel for a living and I can tell you that all of the brands of fuel are mixed together in the same tank once in these large storage facilities and are sold back and forth between brands to meet demand. The only difference in the brands is the additive that is added as it is loaded on the truck.
When on trail learn to drive with MPG in mind. I drive with a constant eye on the 'instant MPG display', when safe, making speed adjustments to keep it as high as possible. If you have an older vehicle without instant MPG install a vacuum gauge, the vacuum gauge has a direct relationship to the position of the throttle.
Get up to speed quickly and reduce speed slowly. Getting up to speed quickly because the shorter time you are getting 2 mpg the less fuel you will burn. Reducing speed slowly or coasting into a stop because this longer your coasting at an extremely high MPG the less fuel you burn. In my case on trail with long descents I notice leaving my jeep in gear with no throttle can give me the best mileage. If i take it out of gear the jeep stops, and if I even slightly touch the throttle MPG cuts by two-thirds. Now this is in a Jeep WJ with the I6 and automatic transmission, your millage may vary on the last trick.
Gasoline engines burn between a half and one gallon per hour idling and all of those little stops add up. So even if you stop for a moment to read a map, shut it down. This is even worse if you are warming your engine at the start of the day, a cold engine is real un-efficient, it will warm up much faster under load. It's much better to just start it and drive easy going until it warms up. Your overlanding, it should all be easy going anyways.
Off road I have found it seems to do best in 4-high with all differentials including the center diff unlocked, only go in to 4-Lo and or lock differentials when it is necessary. 4-high works well because the front wheels will lift themselves in the sand providing less drag to the vehicle. Don't jeopardize safety for this, if you see an oncoming obstacle stop and get into 4LO before you get into it.
Mark