Energy is a interesting subject:
Ask yourself, do you want to charge your laptop (in the van)?
Will you be watching television?
a 60W panel will be sufficient if the only things that use electric in the van are
LED Lights
Water pump
Toilet flush
Phone charger
If you want to start using a laptop or TV or any such thing, 60W will not adequately charge your battery - especially if you plan on using any blown air heaters. Think of it this way, in winter there are about 5 good hours of sun in England, and the panel will be lucky to input about 0.3-0.5amps an hour (in winter)... so basically u can use/charge 2.5 amps per day...
In summer, ull be lucky to get about 2.5-3amps per hour from your panel..
I recommend regardlessly of what size panel you get, that you also split charge from alternator to leisure battery AND trickle charge engine battery whilst you are parked.
I use this to keep my engine battery full:
https://www.kemo-electronic.de/en/Car/M ... 4-V-DC.phpMaplins used to sell it for £5.. can't find it on their website now but possible its still available.
You could also just use a dual battery solar regulator. There are many cheap ones available.
Livin' in me van in Portugal.
'93 Mk4 TD 150L Hitop Custom Camper
100ps Epic blue spot