You can find lots of RV Solar research reading in the Going Green section:
Going Green - iRV2 Forums
You can provably add a second charge controller, but I doubt you will see any additional charging. If you really want it to work properly, you will need to rewire your system to isolate half the panels to each controller. This may not be as difficult as it seams, you could just route one new positive cable and share the 6 gauge ground.
How long has this system been operational?
What is the peak charging amps you've seen so far?