i have not done it yet, but i am currently in the design stage of moving my rear bath to just the rear corner, more similar to some of the newer 23' safari.
since you only want to create a double-bed, and not a king size bed, you may consider this as well.
attached are before-after diagrams. notice that i have the toilet staying in the same spot, it simply rotates 45 degrees so that it faces forward. all the other plumbing and vents would still need to be re-routed, but at least the black water tank can stay in the same position. i realize you may not have my particular design, but there might be something about a corner bath that could work for you.