Clean the bike as well as possible. Use fogging oil as directed - pretty hard with four carbs - or shoot a teaspoonful or so of oil in each cylinder with a pumper oil can, loosely replace the plugs, and kick it over a few times.
I drain the oil and refill it with fresh oil in the spring. There's no benefit to having new oil sit in the sump or tank all winter. Used oil won't do anything except coat the bottom of the sump/tank with sludge while it sits a few months.
Spray WD40 liberally on the chrome, especially the front fork tubes. Coating with grease is better but it's a bugger to get off.
Most storage units do not allow fuel in tanks. You can either coat an empty tank with oil (2-stroke oil is good) or put some mothballs in a sock inside... this displaces air and thus oxygen with the mothball gas and eliminates corrosion even if you have some condensation. The problem is temperature cycling: air gets pumped in and out with temp cycles and the water in air can condense. That's why a full tank is good, there's very little air space. If possible you should keep the empty well-aired-out tank in a heated part of your house somewhere with the cap open.
It's best to let the tires down to about 10psi, put the bike on the centre stand, and prop the front wheel up so there's no weight on either tire. A piece of 2x4 cut the right length supporting under the oil filter is a good way to lift the front wheel.
