Tim and Bob have it right, so let me just amplify a couple points to make sure they are quite clear.
1. Yes, drain the water system, for all the reasons they have said. It also prevents water in the tank from getting "stale" and developing an off taste.
2. Draining is easy, as Bob said. BEFORE you drain, make sure that the ELECTRIC switch to the water heater is off. This switch is outside - if you don't know where it is, check in your owner's manual (page 27 in mine) to find it. Or the same Search that Bob suggested will turn up postings about it.
3. Unfortunately, the issue of leaving shore power attached to the TM for long-term storage (more than a couple weeks) is a push-me/pull-you. If you DON'T leave power connected, then the battery will eventually go flat, which is not good for the battery. If you DO leave power connected, then the converter's built-in charger may overcharge the battery, which is even worse for the battery. To complicate matters, the battery in the 2720SL is inside the rear storage compartment, where you can't get to it without fully opening the TM. This makes it impossible to casually check the water level, or check for bubbling. The best answer - really the only one in my opinion - is to make sure that the battery is fully charged BEFORE you close the TM, and then disconnect it. A fully charged battery can be left alone for several months, and cold weather is actually better for it in this case.
Disconnecting the battery is easy. Open up the rear compartment, take the cover off the battery, and remove the fuse from the holder that is in the battery wire. Or loosen the wing nut on the positive (+) terminal, and pop the ring lug off the battery connector.
Finally, Bob mentioned the "new" converter from American Enterprises (a Chinese importer, ironically enough). As he said, there is very little info available. What little there is hints at a third stage of charging that won't overcharge the battery. But there is not enough info to confirm and I don't know of anyone who has accumulated any real-world experience. Until I know for sure, I won't trust it. The only real answer seems to be the Progressive Dynamics retrofit that Bob performed. There is plenty of information available on this unit, and Bob has accumulated a lot of real-world experience.
Hope this helps.
Bill
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