Out of curiosity... how are you attaching bumpers to the front/back corners? You'll need some sort of frame member extending past the wheel on the corner, but your outside plates appear to stop short.
If it were me, I would add support with some more C or square tubing across the front and back. Bolt it into the existing C channel and into the belly pan.
As an example, here's our custom chassis this year (We've only done a custom chassis once before, in 2009).
