In reply to bobstones:
If you're in a van I can't imagine any need for a generator short of wanting to make a lot of noise or running a laser weapon that exceeds the vans spare electrical capacity.
A couple of decent leisure batteries in parallel and some high current split charge or DC-to-DC charge system (depending on the van electrics) should see you right. Perhaps add a mains powered30A intelligent charger if you'll be passing mains hooks ups occasionally. Although if you're doing that you're either on the mains or driving regularly and split charging.
If you're going to have long periods without running the van up, stick a 100W-150W flexible solar panel or two to the van roof or the ground when parked up (they're 2.5mm thick and bendy so stow much more easily than normal panels) and get a cheap PWM charge controller for them to connect to the leisure batteries. With fuses etc.
Even if you do end up needing a genny (taking an inefficient fridge, microwave and big plasma TV?) you almost certainly want to buffer it via a battery bank to avoid keeping yourselves and everyone else up at night.
Post edited at 20:11