Your first step is to learn about amperage and wire gauge. After that you could research RVs that run on DC.

Then, after researching amperage and wire gauge, pay attention to the fact that power losses in wires from the inherent resistance thereof is proportional to the square of the current passing through those wires:

https://en.wikipedia.org/wiki/Electric_power#Resistive_circu...

Unless we standardize on 380-400v