Hi Marek to answer your enquire about batteries, an healthy battery should stand for a fair few months without any problem, but I would advise you to put a smart charger on which will keep the battery in peak condition and will only charge the battery when the charge state drops, if its left in storage for quite some time.
VW state that you must charge the leisure batteries every 4 weeks. If left longer than that even with everything switched off they will gradually drain. I certainly wouldn’t want to leave without charging for more than 6-8 weeks. Making sure that everything has been disconnected. Definitely no dashcams as they will drain the batteries in a couple of weeks.