I tend agree that exact placement is not critical. This is more food for thought.
Originally, I imagine the propane tanks and battery ended up there because neither was wanted inside the unit. I don't know exactly what industry codes or rules apply. They are also easier to refill. Both benefit from air flow and ventilation, although some batteries no longer need as much ventilation, AGM versus lead acid.
By the way, I preach the see-saw fulcrum theory, and I grant that in front, the hitch dampens the effect, unlike the back of trailers. I'd argue that the span isn't trailer axle
to hitch, but trailer axle to vehicle axle. Even the back of trailers is dampened by the front coupling to the tow vehicle.
Why the hitch tongue? First, it's already there, well ventilated, & somewhat protected between vehicles. it would be far more dangerous to place them at the back of the trailer, where they would increase bounce, lighten the tongue, and be more prone in a rear-end accident.