I was researching aluminum platforms and came across this thread in a google search. I should have looked here in the first place, haha. Your original design alleviated my fear that the modular construction would not be strong enough, but your recent removal of the center support really gives me confidence that the supports are strong. I am guessing you don't sleep two people on the revised platform, do you?
I originally wanted a really light design utilizing drawers, but I came to the realization that drawers, drawer slides and the necessary hardware to make it durable will essentially double the materials and weight.