That's where Little Guy mounted the deep-cycle battery. I thought it was strange, but it certainly is handy. Since it's so close to the hitch I don't think the weight of the battery should be included when figuring hitch weight to gross weight percentage.
Tongue weight empty with that battery there is ~165 lbs. Tongue weight fully loaded is about 230 lbs. (I stash 160 lbs. of gear behind the axle in the hatch and "trunk," which only partially offsets the 126 lbs of a fully loaded tongue box since it's much closer to the axle. Yes, I weighed all the stuff.)
The V8 4Runner's hitch is rated at up to 700 lbs and she sits almost level front to back when hitched to the TD. (it usually sits an inch higher in the back.)
We have no trouble with trailer sway in any conditions, including steep mountain roads and offroad. And in spite of a tongue weight higher than 10% (but less than 15%), with this combination handling is exceptional.
Fully loaded trailer weight is ~1750 lbs. This TD has a heavy duty frame with steel skid plates.
It also has heavy 31" MT tires. I load an additional 300 lbs of gear in it for an extended trip. Again, this combination wouldn't work well with some vehicles, but works great with mine.