unless your fuel is at 100° when you store it in a 65° basement, then you might get some condensation but I've never had it happen after running in 90°+ temps and bringing the cars inside for the night in my Air Conditioned home at 70°F.

Once fuel is mixed at the factory, it will not settle out unless it soaks up too much moisture. Storing in a cool basement in a sealed jug is not going to make it spoil faster whether its on a concrete floor or a piece of wood. I don't see that mattering too much. The key is tightly capping the jug off and keeping it out of the light - nitromethane breaks down under sunlight (and possibly artificial light..?).