Gilles,
Every year, I have to winterized my sail boat. I top the tanks with fuel to
prevent condensation, and I also put an additive in the fuel called Stabil.
You can get this at a marine store. It keeps the fuel from breaking down and
getting gummy. I also lube all fittings.
On the boat it is important for air to circulate the cabin to prevent mildew.
Leave a window cracked open, but watch for creatures crawling in for a winter
stay. Mice love VW engines and can make nest in the worst places.
Also they have marine products that you leave on the boat that will help
prevent  mildew. Keep the fridge, water tank etc. cracked opened to prevent
that stale smell you often get. I open all my cabinets as well. Drain all
water from the fresh water system to prevent freezing.
Once my diesel engine is winterized on the boat I can't start it until spring.
The oil that sits in the engine all winter will have to be changed again
before running it. Oil that sits for awhile (Winter) starts to breakdown and
contaminate. I guess if you start your Westy once in the while, that won't be
a problem? Other tips are covered by other owners so I won't repeat them.
Good luck and don't forget to say "hi" to your Westy once in awhile during
those cold lonely winter nights.
Dan
87 Syncro
85 Westy
71 Bug Conv
35' Cheoy Lee sailboat