Staceman - also re: the top (sorry to pull thsi o/t), when you have that 1/2 top on there, are you usin ga different rollbar? From (what little I can tell in) the pics, it looks like your rollbar bends back into towards the cabin at the top. fitting the angling contour of your top. But normally it sticks out the other way (as in yer 1st pic w/ Can-back.
Am I just confused in the angles or did you do something to that too?

BTW to get back o/t, for the box, I wonder if you were to use aluminum instead of wood if it would help alot w/ the weight. Then to limit the (potential) noise and add some strength, line/glue it w/ Dynamat style rubber or something, then the velcro padding on top of that.