Hi, and welcome
Like many other topics I'm sure that there are differing views on this.
The 'belt and braces' view would be to drain everything down (boiler and fresh water) all the time between Oct - Apr...just in case of early/late frosts. You can even get gizmos which blows out any residual liquid in the pipes too (as advertised in MH magazines)
I do something similar to you though: I am draining down my boiler now but tend to leave my fresh water tank UNLESS there is talk of a heavy, frost/freeze...then I would drain down the fresh water too. If we do get a 'beast from the east' scenario I would probably plug mine into the mains and get some heating on inside it plus I have a fresh water tank heating element which I can switch on. I've not needed to do that yet mind.
If in doubt, I'd drain and air on the side of caution. The previous owners of our last MH didn't drain and they severely damaged the boiler which packed up on us in Poland about 4 years ago! Frost damage had damaged the heating fins internally and ruptured the outer casing to, which meant water escaping inside the MH (under the bed!!).
I am assuming that your grey water is empty also?
We have our MH on our drive so can respond quickly if required plus we tend to be away in it every 2-3 weeks throughout winter and also go to Soain for 2 months in Jan, so escape the worst of the weather.
Graham