If you're using vinyl replacement tubing, cut the copper line somewhere under the bed, and slide it out through the rear compartment. You can do the same with the copper lines under the sink, just unhook it from the sink and pull it out.
To put it back in, slide the replacement in through the rear compartment, under/behind the shower, feed it along through the side compartment under the bed, and up to the sink area. You can so this with both hot and cold lines.
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.