If you are looking for a storage bag for the winter months, here is what I use. Since this post, we have a lift to store both of my cats and they both get bagged!!This is from a previous post:
Here is the link to the company that sells the CarJacket and the dessicant tubes:
http://www.carbag.com/
We chose this type of bag because it is our understanding that the fan-inflated bubbles circulate available air that has high relative humidity. Those bags are generally clear and allow any ultra-violet light to penetrate. Our research indicates that the translucent CarJacket, along with the 20lbs. of dessicant (the bag comes with 10 lbs.) is the optimal solution. The darkness and inert atmosphere in the bag work especially well. We find that the 20lbs. from the beginning of Fall storage weighs 30 lbs. when we "let the cat out of the bag" in the Spring! That means approximately 1 1/2 gallons of water was removed from the controlled atmosphere!
The dessicant can be re-used by drying it in the oven just before re-use. It comes with instructions on how to do that.
Also keep in mind that if you use one of these fan-inflated bags to store your car for the winter and it is in your daily garage......any moisture and/or snow that is dropping off your other vehicles as they are parked in the garage is also being circulated by this fan into the bubble where your car is stored.
Of course, this is a matter of choice and this is just our opinion based on our extensive research.
This is the third winter for our CarJacket and my cat is just as good as new. I know that other people store their cats for the winter without any of these bags and say they have not had any problems. We prefer to not take any chances, but then we store it in our daily garage!! 
We also know of another source here in Michigan that is a authorized dealer for the bags and will sell them to the Prowler Owners at a discount. Email me if you are interested.
In addition, following is the link for the Battery Tenders that we purchased. There are many different kinds, being sold everywhere, but this is the best deal we found anywhere! They are usually sold retail for approx. $59.95. As you wil; see when you click on the link that they sell theirs for $33.95. It is the one with the Order #01991.
http://www.accwhse.com/batteryt.htm
Here is the procedure we follow every year:
I'm in Michigan also, and here is my procedure for storing the cat:
We fill the cat with gas, adding fuel stabilizer at the gas station - drive the cat back to ensure the stabilizer reaches throughout the fuel system. Full tank of gas minimizes the amount of air in the tank, minimizing oxidation of the fuel.
We use battery tenders because they monitor battery voltage, only charging to maintain a full charge, never overcharging. Battery Tender just released a permanent bleed for the battery and with a cap to protect the connector. Also change the oil and filter before storing it. Air the tires to the maximum pressure on the sidewall, making sure to remember to lower them to the recommended levels in the Spring.
In our climate, cold winter, high humidity, stored in a garage that is used daily, we elect to bag the car. There are many types of bags. The best solution is a black plastic bag and large quantities of dessicant in the bag to remove all moisture within the inert atmosphere. When the car is removed, it is absolutely as clean as the day it was put away with the engine starting faster than I would care to have.
We thoroughly cleaned the cat, making sure it is completely dry before putting it in the bag. Also making sure that it is waxed and detailed. We cover it with its normal car cover before putting in the bag. It is a type of bag that zips on three sides. You drive the car onto the bag carefully. Distribute the dessicant tubes under the hood, in the trunk, in the interior and in the bag. We used 20 lbs. and extracted 1 to 1 1/2 gallons of water. Then we put on the normal cover so that the bag doesn't scratch the car if it blows around at all. We put on the battery tender and zipped up the bag. When we took it out this Spring, it was as clean and beautiful as the day we put it in.
