A question on rolled shore power cords

The basis for many electrical capacity determinations is the ability of the item to shed heat resulting from current flow. As the temperature of a wire increases, so does it's resistance and associated voltage drop. A long, coiled, light gauge electrical extension cord carrying a greater load than it is rated for can get hot enough to melt the insulation. Most trailer cords do not seem to reach this condition being properly sized for their load.
If you want warning for this particular event I would suggest you get a plug-in voltage monitor with an alarm function.