To clean: use water and Windex and a Scotch Brite Dobie all-purpose cleaning pad. Can also use any plastic pad that doesn't scratch glass. The pads can be bought at most places where better sponges are sold like supermarkets or Lowes.
The benches can be left out all year long in temperatures as low as 10 degrees F. If left on a porch or covered deck they can stay out in even lower temperatures.