I did my 3012 about 3 weeks ago.
In order to get better access, I pulled the whole panel inside the storage compartment down since I couldn't "fish" out the suction hose for the antifreeze, and it is much easier to get your hand on the valve to cut off the fresh water line from the tank. It is only a few screws and a little twisting of the panel to get it out from behind the heat duct that runs up thru the middle of the storage compartment at the rear wall. While I had the panel out, I vacuumed out the small amount of sawdust and debris that were left in there, as well as re-checking the connections on the hoses going to the docking station.
The valve for the water heater bypass is on the water heater, under the sink, easy to access it thru the door under the sink. The valves on the inlet and outlet of the water heater are accessible from the living room side door.
I blew out my lines before I winterized.. including the black tank flush.
*Edit* I should have said I pulled 1/2 of the wall panel down in the compartment since it's in more than one piece. I find the access panel wasn't put in the most easily accessible place, it could have been moved lower on the wall panel for better access and perhaps a little closer to the systems you are trying to gain access to in the first place.