The Terrapin is able to accommodate a crew of two, why is there only one bed?

It's a small, military ship. The UEE design brief didn't include lavish creature comforts, and as a picket ship, the military expects at least one crew member to be awake and on duty at all times. How much good is a picket if the whole crew is asleep? Civilian operators might think differently, because they may be using their Terrapins as explorers, but Anvil designed the ship for military use.