After Harry got over his shock at receiving something from his parents, he expanded the trunk to full size and went inside. On the table in the den was the second letter. He grabbed it, sat down and read it.
The Potter trunk library was better than the Hogwarts library. Those books deemed not suitable or restricted at school was fully accessible in the trunk. Also, the potions lab was better stocked than Snape's classroom. Plus Snape wouldn't be standing over you, yelling insults at you, while you practice your potions. The study room/den was a nice and quiet room to read or study without interruptions. It could easily turn into a sleep room if needed.
Harry looked around the various rooms and through about it. Given a kitchen & loo type room and one could live in the trunk.
What would be your reason of creating such a trunk for your child? Write down your answer as a story and submit it for the Challenge.