I had my 453 stored away from home for two months and two weeks recently. I stored it with three bars remaining and tyres pumped just under max pressure. It was in a garage, so no cover. I didn't start it at all either. At the end of the two months and two weeks, I got in and drove it away, no issues to report other than flat spots in the tyres that went away after a few minutes of driving.
The 453 and the 450 won't be driven during the winter (seeing what these Chicago winters have done to my 451's subframe is saddening) and will sleep in my garage all winter. It seems the 450 is more quirky than the 453, so I'll just start both every 30 days. The 453 has 4700 miles while the 450 has 24000 miles.
It seems the only car in my fleet that has issues with long term storage is my 451...but 135k miles on the original battery and as of now has spent most of its life outside, so not surprised.
I'd recommend a battery tender just to be safe. For a car cover, I'd make sure you get a form fitting one with a soft internal fabric. Super cheap eBay ones will scratch the heck out of your tridion cell (don't ask how I know).