Hi Jerry,
I don't know what your couch is like but what other choice do you have? If you are careful I know you can do it. That's the difference between rip and tear and disassemble.
I would guess that if you know what Pex is you can fix the leak. It may just be one hole where you can just replace that section. if it is in the lowest spot probably a crack from freezing, and probably more than one leak. If Pex won't work the plastic line is available at mobile home dealers or camper supply places and isn't real expensive. I hope you are lucky and only find one bad section. It might even be a loose connection.
They make a fitting to screw on the water connector that you can blow out the line which is also good for finding leaks without the water damage.
Good luck and report back when you find it.
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