Here is some information I have non my Moen Single Handle Shower Valve, but I don't know if your RV uses the same type.
Moen guarantees there products for life so if you find your shower cartridge looks like mine then maybe Moen will send you one for free?
SHOWER VALVE – 2004 ITASCA HORISON
According to the Winnebago Horizon Parts Manual, my coach takes the Moen 62300 model pressure-compensating valve. (But you need to verify this!)
MOEN Shower Handle:
Note: I have never replaced my shower cartridge, but I keep this information in case I need to. My notes also include the following picture of a shower cartridge but again I do not know what your RV Moen Model number is. You can call Winnebago with your coach serial number and they will tell you or you can look at your RV parts list... with your serial number.
Do you know how to find your RV parts list? If not go to these websites:
Service Parts List