I have a '74 Argosy and believe you have a similar BW tank.
I did not have to remove the inner skin. The toilet must be removed along with any cabinetry above the tank. Mine has a hose clamp on the outlet of the tank which must be released. Remove the box surrounding the tank and it will lift up and slide out of the sewer connection.
Post a pic of your setup. It will help.
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