Best way to maintain Motor Caravan batteries over Winter.

I might be buying a replacement Motor Caravan and would not expect to move the Motor Caravan for months at a time over the winter. I placed neither the vehicle or leisure battery on charge and as a result the Motor Caravans would not start as. I think that the mains Hook-Up only charges the leisure battery and that I would need to drive many miles to keep the vehicle battery healthy. I recently came across a few mentions in the Motor Caravan press regarding “Smart Chargers” but have no idea how to install one or if they need to be permanently connected to mains electricity. I do not fancy removing the batteries in order to maintain them in the garage by charging and checking them and would welcome a suggested method to ensure both the Motor Caravan batteries are kept in a healthy state.

Ensure they are fully charged and disconnect the negative cable.