[Bastien]

Hadn't thought about storing the plywood under the two main beds...

This middle 'bed' will have to support at most 60-70 pounds, the typical 9-10 year old girl.

I'm thinking it needs to hold 400 pounds or so. Four 70 pound kids jumping in the middle!

I was thinking the center panel hinged to one bed, with a channel iron or hooks and pockets connecting to the other bed. When not in use, disconnect them and it swings under and stores underneath. The safety rails could sink into the pockets.