Rust in fuel tank

[CDXXVII]

Lets say you are storing your car/truck and the gas is not full. There is an air space that holds humidity and causes rust right?
Has anybody heard of a desiccant pack that is meant to be temporarily hung in the fill pipe to lower the humidity of the tank air space?
I found this device but it looks like it is meant to be submerged in the fuel.

http://snowcitymi.com/catalog/index.php?main_page=product_info&cPath=7_156&products_id=48

[machoneman]

Never saw on of those....who knows, it may work.

Have a different idea though. Years ago, I worked in the bulk chemical trade (tank truck/rail transport) and learned a lot from experts in the manufacture and storage of a wide variety of fine chemicals. Many are stored at refineries or other sites with a blanket of nitrogen displacing the air that normally would be in a partially filled tank. Rust can't form in the presence of nitrogen.  One could easily rig up a spare gas cap with a Schraeder valve and introduce 1 psi of nitrogen gas to the tank. Once done, seal up any tank vent(s) until Spring.  One has many sources these days for bottled nitrogen that tire shops offer.   
 
On second thought, some welding gases like argon would also displace air. 

[My427stang]

This doesn't answer your question directly, but I am forced to store my Mustang in my trailer over the winter, go figure, garage can fit 5 cars but my wife and daughter wont park outside 

I put it in the trailer, then in a car bag. http://www.carbag.com/buy/car_jacket.html

The car bag is sealed, and you place desiccant bags all over the place.  It stays dry as dry can be.  Aluminum stayed pretty and I had absolutely no issues despite severe temp swings, rain, snow, etc.

Matter of fact, I threw some Stabil in there, and when I took it out for the spring, I just topped off the tank and ran it. 

[FOMOGO]

I just top off my tanks and disconnect batteries before I leave for the winter. Never have any issues. I live in a pretty dry climate, but I think this should work anywhere. Mike