You can open the doors every day for some natural ventilation or install active ventilation that uses fans to pull outside air in and push the stale air out. The latter is probably preferable in winter, although it all depends on what you're able to tolerate I guess.
As for rust, I haven't experienced any significant amounts of undercarriage or panel rust on any of my 20+ year old vehicles in Western Europe, but we don't get as much snow (and salted roadways as a consequence) as Scandinavia does. You can look into undercarriage coatings for this though.
You can open the doors every day for some natural ventilation or install active ventilation that uses fans to pull outside air in and push the stale air out. The latter is probably preferable in winter, although it all depends on what you're able to tolerate I guess.
As for rust, I haven't experienced any significant amounts of undercarriage or panel rust on any of my 20+ year old vehicles in Western Europe, but we don't get as much snow (and salted roadways as a consequence) as Scandinavia does. You can look into undercarriage coatings for this though.