Sounds like you have a pretty good storage plan. The Battery Tender will be your best ally.
When the top folds, it bends the hydraulic lines. Since you probably drive it more with the top up than down, I think storing it with the top up is a good idea and places less stress on the lines. Over time, they develop a memory so I would want mine to want to be as straight as possible, since that's their natural state of lay. (Hmmm, that doesn't sound right. . . ) From all of the owner reports I've read, if a hydraulic line breaks, it seems to happen more at one of the bends where it has a better chance of chaffing, not at a fitting.
Depending on where you live, humidity may be a problem. I used to live in Seattle, where you don't tan -you rust. I used a product in a motorhome (that was heated at all times when stored for the winter) that used granules that soaked up moisture, then disolved once saturated into a container. I had to replenish it about once a month, and the container held about four cups of water.
If it's dry where you're at, cracking the windows a bit (since you're car will be covered) can keep it from smelling up. I had mine stored for a year like that and still had to use a product from Griot's (Stinky Be Gone) that used chlorine gas or something to wipe out any and all microscopic life forms. The car was sterilized after one night and smelled pretty darn clean afterwards. Good stuff if you ever need it.
Give the leather a good cleansing and protect it prior to storage as well.
While you're at it, this is a great time to inspect/replace a major safety item: the lowly windshield wipers. I switched over to Bosch Icon wipers a few years ago; --if you ever hear of a better wiper, let me know. These things work exceptionally well. Long life and no missed sections of the glass. What more could you ask for in a wiper? They even have airfoils to ensure they stay pressed against the windshield. Very well thought out product and highly recommended.
Do inspect the drain in the trunk compartment prior to storage and every three months thereafter when driven regularly. You should be able to see the garage floor through the tube (or hole on later models.) This is the best advice I can give any XLR owner. It's quick, easy, free and can save you a small fortune in repair bills.
Before closing the top, apply protectant to all of the rubber seals. This includes the doors, rear decklid, windshield header and anything else you can get at. GM recommends Krytox which isn't cheap but works well. It's more of a lubricant, and great as a squeak suppressant, but it should keep the seals pliable and minimize any deterioration while it sits, waiting for you.
Some car fanatics like to store their cars on rounded blocks to keep the tires from developing flat spots. I'm not that far gone yet.
And obviously, you want to give it a painstaking wash, polish and if possible, clay it after the wash. When you pull the cover off (and it WILL slide easily after being clayed) in the Spring, it will still be beautiful and as ready to go as you are! I'm a Zaino fan, but there are plenty of other great cleaning products available.
I'm sure others may chime in with their tips. These worked great for me.