If I understand you correctly, you are proposing that rather than using a seperate cart to move your robot from the pits to the field that you will pin casters to the bottom of your robot chassis, thus using the robot itself as the structural part of the cart.
This is an excellent idea. We used to do that with our robot when we competed in Toronto, as it saved shipping an entire robot cart out to the competition and back. I see that our trip to Toronto, however, a five hour flight, was a mere hop, skip and a jump compared to what you have ahead of you!
You
may have to remove the casters in the staging/queing area and carry the robot on to the field, but aside from that I can't think of any rules preventing you from doing this... at least as I understand what you are proposing.
Jason
p.s. There aren't many rules on carts...
http://www.usfirst.org/uploadedFiles...e%20Events.pdf section 4.3.2 about covers it.