The fresh water tank is located under the bed, along with a large storage area. Access to this are is by lifting up the platform the bed mattress sits on.
Fortunately, the platform is hinged, AND, it has gas springs on it to help lift it, then hold it up.
These springs go bad over the years, as I’ve replaced most of them on our Southwind.
The springs for the bed are SL34-110. I purchased 2 replacements on e-bay for about $15 each (including postage) (CLICK HERE)
Squirt a little silicon lube inside the ball fitting, this makes it easier to snap the new gas spring into place. Give the shaft a squirt of lube also.