Most DIY’ers who wire their van don’t think about the possibility of a fire. But it can happen if you use the wrong size wire.
Without going into theory and all the technical stuff; think for a moment what you know about an electric heater.
When you look inside the electric heater you see wire. It could be straight, coiled or whatever. But when power is turned on and electricity is applied the wires glow.
The more current/voltage applied the brighter and hotter it gets.
The knob on the electric heater, in theory, is like adding more electronic devices to a wire. The more you add, the hotter the wire gets.
Be mindful of this when you are planning and wiring your van. Here are some articles that may help you.