It is actually very simple to figure out what do you gain if you keep i gallon of water in you smoker. Information is simple to get, and math is simple to figure out.
With one gallon of water in your smoker:
If your objective is to keep your interior temperature above 212F, the water will fight your attempts because water does not want you to go above 212F. When you see your gallon of water has been boiled away, you would have wasted about 7800 BTUs of heat to sustain temperature
If you left your smoker door open too long and temperature drops below 212F, the water will help you to recover by giving you only 16 BTU for every degree F increase, until the temperature gets to 212F, then the water will fight you to get any higher.
Meanwhile your 1,800 watt heater can give you 6,120 BTUs/hour.
It is a thousand times more complicated to come up with the best rub for your ribs.
dcarch