Is it crazy to leave water in your tanks in storage?

It is only as crazy as you think it is.

1/2 full probably won't hurt anything, but also unnecessary. The seals you're concerned about are at the very bottom of the tanks. I just pour enough antifreeze into the tanks to know some got down to the drain valves. I dump some in the toilet to keep that seal wet, and a bit into the drains.

Water wont keep the seals pliable. They will be fine without anything in the tank.

You're storing your rig in Las Vegas. Gambling with the weather is your choice.
Personally, I would drain the tanks and use RV Antifreeze as recommended above.
Then you know the tanks won't freeze in the event of colder than normal weather.

When I gamble in Vegas, I lose. :B
Why gamble on the weather, drain the tanks and winterize.

rv2go wrote:
When I gamble in Vegas, I lose. :B
Why gamble on the weather, drain the tanks and winterize.

If people didn't loose, there would not be those big fancy casino's. They plan on you loosing. keeps them in business.

Keep in mind that if you leave enough water in the tank to fill the shot section of pipe going to the drain, it will freeze and bust the pipe.

There's no need for the gasket material to be kept moist with water. If you think about it, the seals on the output side of the valve (which are the same material as on the input side) are dry practically all the time, or at least should be. The whole point of the gasket, be it rubber or silicone or whatever material they use, is to be impervious to water as it seals.

Crazy? No.
Silly and/or unnecessary? Yes.

This is a great plan...if you want to learn how to do plumbing repairs.