If I'm looking at the right photos of your model, your kitchen is raised (in the rear) and you have a huge storage space under the floor with a rear outside access. The kitchen floor is framed with aluminum. The Aluminum is framed to the bottom floor of the camper which then sits on the actual main frame.
In actually, the weight of your refrigerator is NOT directly on the 2 main frames supporting the entire length of the camper. It's sitting about 2 1/2 or more feet above the main frame on an aluminum supported floor.
Is this correct:
If this is so, then yes, I can see where over time the bouncing up and down of the rear of the camper with the weight of the refrigerator sitting on the very end could weaken or even break the aluminum supports under the kitchen floor.
How you would support or strengthen it would be a different matter. The weak spot is not with the 2 - 12 inch frames. They will support the weight just fine with any bouncing. You'll need to add support from the bottom floor to the kitchen (upper) floor.
I think if it were mine, I'd use a metal beam across and then an upright from the bottom to the top floor to support it independent of the trailers aluminum framing.
I can see in time, you'll have floor separation or broken aluminum frame welds under that refrigerator floor.
Good luck.
(Now.... if the camper is parked stationary and never moves, you'll have no problems, the problem will be ONLY if you travel and those horrid bridge transition joints on interstates that tear things up inside the camper... there is the problem).
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2019 Montana High Country 375FL
2014 Chevy Silverado Duramax, 6.6L Dually