Storing camper over winter

Hi,
Due to a family bereavement, I will need to safety store a camper van this winter. I'd be so grateful if someone could advise the key points. I assume I will need to get a trickle charger so the battery wont die (although it has 2 batteries...a leisure and the engine battery)...or can I take out or disconnect the batteries instead?
I have the option of storing it in a shed or in a barn. I'd be most grateful of all advise as I want to make sure its taken care of properly.
Many thanks in advance
Lisa

As Allys says and drain your water so frost isn't a problem

And remove all foodstuffs unless tinned to reduce the possibility of a rodent infestation

Thank you so much for your reply. I think the best option is to remove the batteries. This is a silly question but would it be enough to disconnect them? Although, they would go flat I guess.
Would you recommend removing them and connecting them to a trickle charger? I read that online somewhere
Also, time for another stupid question!!! (I'm a complete novice!)...is it possible there is a 3rd battery somewhere? Where should I look?
I feel stupid asking but better safe then sorry!

Thank you so much for your advise!
I wonder is it necessary to place a storage heater inside the van for condensation? Or maybe thats a no no!
I know people do that with a motorbike, they place a small heater under the winter cover to avoid rust, but maybe thats a different ballgame

Well said Liam, add if you give an idea of where you are someone might offer to have a look with you.