Hi Paul.
I have my two interstate batteries in the basement for the winter, or until we venture out again.
I bought a charger called a Battery-Minder. Here is their link:
http://www.vdcelectronics.com/batteryminder_12112.htm
I have both batteries in maintenance mode with this charger, and I think you can do up to four at a time. They cost about $50.00
This last fall I also bought a set of tire protector/covers for winter storage to protect from UV.
If you get the tire covers from Camping World, then this is exactly what you need: Camping World "Adco ULTRA TYRE GARD" NUMBER 3. These are the ones they sell for tire diameter of 27" to 29"
Harm coming from batterys on concrete is apparently a myth. This coming from interstate.
We keep the shades closed to minimize damage from sunlight exposure.
Best.
Jonathan