Housing: there are some places that have abandoned buildings like castle and monasteries that I've put on my list, otherwise we'd have to look into tents for the timing being. Fresh water: I'm trying to locate places with fresh water access. Access & security: there are warding experts here. Aurors have traditionally provided security for prisoner transfers, we can train people to act as guards. Once the Death Eaters don't have their wands or weapons they're just your average bare-handed psychopath.
Those are my initial thoughts. But until we find a place that is actually feasible, I haven't thought much past that.