While you are at doing the replacement, i would highly recommend you replace the plastic 90 degree elbows on the two water lines to the mixing valve with brass. They get brittle over time, or crack because they were tightened to much during building the coach. You may also want to replace the plastic water lines with Braided Stainless kitchen faucet water lines , down to the basement. I had a elbow fail, causing $$$$ damage to the tile sub floor.
You may have to find the blind panel that must be removed to access the back of the mixing valve. Usually a wall by the panrty, or galley. Fasteners usually found in the 4 corners area of it.