Never had a problem starting my gen in reasonably cold wx as long as the batteries were OK and proper oil was in the gen. (Oil can be like hard greese in extreme cold so suitable oil must be used so engine will crank) In general key is keeping batteries charged or capable of providing power at low temps. Some people use battery blankets.
In extreme cold wx, people use propane or other fuel powered heaters to warm up any engine to make it easier to start. I have used portable heaters on many engines, including aircraft engines for starts in extremely cold weather,
Have not started my RV gen colder than -30C. But I have experienced temps of greater than -50C (about -58F) 7n the arctic and generally when it gets that cold, you just don't shut down while the vehicle is outside. Could not imagine running my RV in those temps and never had an RV in an area where I have experienced -50C.
You can get dipstick heaters for cars, not certain how they would fit RV generators. Have not seen any Generators with block heaters but I see no reason why not,