Our design evolved from a separate tongue box into a "utility compartment" built into a ten foot long tear

Mainly, we wanted to be able to sit up in the cabin and not worry about our heads dealing with the curve. The utility compartment goes up to the start of the curve. The volume in the curve above the compartment is behind our headboard and accessible from the cabin. We use it to store nature books, park guides, reading material, and sometimes a DVD or two.
In the utility compartment, we have the air conditioner permanently mounted, and we store an Eazy-up, a folding camp table, two folding camp chairs, a privacy shower tent, rubber mats to put under our cabin doors, an extension cord (for when we have shore power), rope and tent stakes to secure the Eazy-up when it's windy, a mosquito net, the crank to put down the legs, chocks, a leveling block, a hitch lock, and a wheel or pad for our tongue jack.
Of course, everyone wants more storage, and the only reason we don't add a true tongue box is the front compartment door, which we open when using the air conditioner. It's located off-center so we can add a propane tank on the front.
Of course, the downside is our galley isn't as deep as it would be. We keep the cooler in the back of our truck, and sometimes a plastic bin with more food. That way, our lunch is automatically with us when we drive from camp to explore. Also, the food is away from our sleeping area: As an old cold warrior I'll tell you, and as events the past few days prove, never trust the bear!
Tom