Electricity going through wires generates heat and that heat dissipates out of the wire losing that energy. The longer the distance of the wire, the more energy that is lost. To preserve that energy transfer, the farther you go, the thicker wire you need.
For example if you wanted to put your solar charge controller (that was handling a 10 amp load out) 100 feet away from your solar panels on a 12 volt system, you would need a 2 gauge wire. If it was 10 feet away you would need a 12 gauge wire.
On a 24 volt system the wire size for 100 feet would be a 4 gauge wire, and for 10 feet is a 14 gauge wire.
This is because the higher the voltage the less energy loss through the wires.
When it comes to your Inverter coming off the batteries you need thick cable period. At 1000 watts continuous you need at least 4 gauge cable and not to go more than about 6 feet. It is better to run an extension cord out the 110 side of your inverter to your appliance than to try to move the Inverter closer to your coffee maker (farther away from the batteries.)
So when you are considering what RV off grid power system to use, one of the main considerations is going to be how far the wires must travel, because the thicker the wire the more the cost, as well as they can be bulky and awkward and hard to manipulate into your components.
The link below show you the amps you will be using in column one, how many feet you will go across the sheet, then look up to the top to see what size wire you need. Always round up to the next distance of feet. For example if you have 25 feet of wire at 10 amps and 12 volts, choose the 33 feet column and it's corresponding 8 gauge wire.
Copy and paste the below link into your browser to look up your wiring thickness needs.