Designing an electrical off grid system for winter

I’m currently planning the conversion of a panel van into an RV including heating, water, and electrical.
The part which I’m not confident about is the reliable supply of electrical power in the winter months in central Europe (latitude: 48°).

The van will be used starting from September onwards and I’m thinking about skipping the installation of solar panels until spring and using the saved money on extra batteries. The batteries could be charged by the alternator of the van while driving and it would be possible to charge halve the batteries on the grid and switch the batteries once a week.

My electricity consumers would be:

• 1 phone charge 5Ah
• 2 laptop charges 15Ah
• lamps run 10h 15Ah
• water pump 4Ah
• heater 20Ah

Which comes to a total of ~60Ah a day, 420Ah a week.
I’ve read that a 100W solar panel will on average produce about 6Ah a day in winter.
Considering that the panels have to be mounted flat on the van and have a higher chance of being partially obstructed because of the low height compared to buildings, is it viable to use solar for electricity generation?

Is there some mistake in my thinking or rough calculations or am I right that there is no chance to live off the grid during the winter with my guesstimated power consumption?

My actual consumption is likely to be less because I would be able to charge the phone, power bank, and laptop from grid power most days (work) but ends would still not meet and I’m probably forgetting consumers.