My Monaco was set up as Doug just explained, two outlets behind the refer, one inverted and one straight shore power. If you stuck your meter into the inverted outlet, you will often get funny reading like you did.
Monaco often used fuses for multiple tasks. You may not find a fuse labeled refer. It may be labeled something else and is sharing the duty. You need to take your volt meter and hit each fuse in the panel.
Don & Mary
2019 Newmar Dutch Star 4018 - All Electric
2019 Ford Raptor Crew Cab