[alsuren]

I noticed that in the photos they're all sitting above the bit where the reinforcements are at the edge of the bed. I couldn't see any reinforcement in the middle, ~but there might be some on more detailed plans~ the videos on their site don't show any support either, but I am willing to believe that the load can be distributed by the pair of cardboard sheets.

You would hope that the 350kg is from a point load in the middle of the bed. If anyone finds out, I would also be interested to know.