In reply to Jon Thorne:
> We're hoping to avoid using campsites etc where we can, hoping to get some advice on good places to keep the van overnight
When I was there, plenty of vans used parking areas down near the dam. And a friend stopped in a van somewhere up the access road to Poema de Roca. A quieter area than down near the dam, which is close to the village centre.
There seems to be plenty of options anyway, and vans are quite common.