As I've suggested in earlier posts the Hull C design from Star Citizen would be perfect for us. When not in use the ship closes up so it can go faster but when carrying cargo both ends extend and cargo is then clamped to the outside
That's the ticket. You could even turn it into a budget liner by attaching habitat modules.
Or as any other container hauler load a whole host of specialized containers such as refrigeration, hazardous materials, tank modules, etc.