Greetings from Colorado!
First of all. if you have a water tank in your trailer, ALWAYS empty it before you store the trailer. I usually open the drain valve on my last stop before coming home. This sloshes the water around and gets virtually all of the water out of the tank. I leave the drain valve open when the trailer is stored, that way, any water left in the tank eventually evaporates.
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To clean a tank, here is a method from
http://www.horsemansdepot.com/common/installation_sanitizing.asp
To assure complete sanitation of your potable water tanks, it is recommended that the following procedures be used. This applies to new systems, tanks that have not been used for a period of time or tanks that may have become contaminated.
Prepare chlorine solution using one gallon of water and a 1/4 cup of Clorox or Purex household bleach (5% sodium hypochlorite). With water tank empty, pour chlorine solution into tank. Use one gallon of solution for each 15 gallons of tank capacity.
Complete filling of tank with fresh water. Open each faucet and drain cock until all air has been released and entire system is filled.
Allow to stand for three hours. -- Drain and flush with potable water.
(Important)
To remove excess chlorine taste or odor which might remain, prepare a solution of one quart vinegar to five gallons of water and allow this solution to agitate in tank for several days by vehicle motion.-- Drain and flush with potable water.
(Important).
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I have a 12 gallon tank mounted above and slightly behind the axle. It is flanked on either side by a 6 volt golf cart battery. The batteries are HEAVY and coupled with a full tank, add about 200-225 lbs to the trailer weight. This low centered weight, riding above a torsion axle with about a seven foot track makes the trailer corner like it is on rails.
I generally leave my tank empty until I come to the "last town" before my camping destination. Since most of my traveling is done in and around the mountains, I don't want to haul the extra weight. I ALWAYS keep 3-5 gallons of water in gallon jugs when I travel. Also, I freeze at least two of these gallon jugs and several two liter bottles of water to use as "ice" in the coolers. This way I have have ice cold water available as well.
I prepare a LOT of my food at home before a trip. I vacuum seal the food in varying portions and then freeze them. I use these frozen food packets in the cooler as "ice" as well. Drop the packet into a pan with water and heat. When you are done with your meal, the water you heated the food in will be just about the right temperature for doing cleanup. Keep it simple.
George T.