Off-grid road trips become easier to manage when you stop treating every category as separate. Fuel, water, power, food and route timing all affect one another.
A good planning flow starts with duration and route difficulty. From there, you can estimate fuel cost, refill timing, power demand and what kind of daily camp routine is realistic.
The most common weak point is not one dramatic failure. It is usually a stack of optimistic assumptions that all lean in the same direction.