Blackout lining can develop a permanent crease if you compress it tightly for too long, so a loose fold and a garment box beat crushing it into a small bag.
Pro tip: Take a quick photo of each window with its curtains hung before removal, so proportions and rod height are easy to match at the new place.
Watch out: Compressing blackout curtains tightly for a long period can set a permanent crease in the light-blocking lining, pack them folded loosely rather than crammed into a small box.