It should be fine if the outlet is constantly energized.
I have my #001 Carrera GT plugged in at work with a Porsche battery maintainer.
I think the most important thing is to use a maintainer instead of a trickle charger. A maintainer cycles the battery through loads and charges. A trickle charger can fry a battery if you leave it connected for long enough as I have found out before(dry plates w- boiled away electrolyte)
If it's good enough for a Carrera GT I think the Elise will be fine. My #001 car leaves for Neenah, WI. in a few days. My #002 car arrives in January and is destined for a home in the L.A. area as most will I'm sure....
Much better to use a battery tender for keeping the battery up to snuff than a trickle charger, no risk of boiling away electrolyte or such. I've been using it for years on my bikes and works very well, made by Deltran.