I put in 1/2" EMT support bars in the cargo bay area
to provide more even support under the thin plywood decking that I intend to attach in this area.
In conjunction with all the tubing underneath,
This area should support a fair amount of weight.
If the wheels can support it, that is.
I've placed my entire 250 lbs standing vertically on this area and the only sag I noticed was in the front shocks and front wheel.
Here's what it looks like at this point. Next step is the steering.