Building a Couch riser

[KingRadicalPhil]

Hi folks, I'm planning to build a riser for my rear row of seating, and I'm looking for suggestions. A few searches seem to indicate several people have built risers, but I wasn't able to find specifics.

Anyway, the idea I have in my head is to use 2x10 0r 2x12 topped with 3/4" ply. The 2x10 or 2x12 would run all around the outside, and also cross brace about every 18", so the frame will look kind of like this from above: (some imagination required):


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I'm a little worried that a fully loaded couch could have as much as 600lbs of people sitting on it. Is 3/4" ply sufficient to support that much weight? The couch has 4 feet, each of which would not have direct support from the 2x10 underneath.

To address this, I was thinking I might add 2x4 bracing as well, so it would look something like this :


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Is this overkill? I worry that maybe I'm overdoing things a bit and it's going to end up weighing so much it's impossible to move it into the family room


Thanks in advance,