What Is This?

Thanks all! I think I've also noticed this box under some RV island beds.

It is the fuse box,

Here's below the seat, shows the back of the fuse box and the storage tube for the table leg.

Agree with above. Ours has two latches you can turn with a coin in the top left and right corners and then the top half of the panel holds down on a hinge to reveal the fuses etc

Power center, has your 110-volt breakers, 12-volt fuses, and convertor

That's the fuse box (and I think the Power Converter is in there too) -- press in on the top of the cover and it should release the latch. The latch on the one in the Cruise America unit I rented was broken and it was duct taped closed.