Auto-collect while offline.
Not a permanent option, just to perhaps prevent collector raids at the cost of gems. Your collectors would give straight to storages for like 12/24 hours at the cost of gems.
Another idea would be to 'appoint' builders to a collector and they would deliver to storages for you. This would be potentially less over-powered as it is limited to max of 5 collectors.
However, it doesn't make much sense for a builder to do this, so instead another gem-costing system could work for a resource manager or something similar. You would buy huts(like builder huts) for more of them and they could be used to deliver collector resources while you're offline.