balance is not the only issue with fuel and batteries, there was an instance here roughly a year ago where a modeller thought he saw smoke from his flight box, he went to investigate and it exploded in his face, 1/2 a gallon of 5 % nitro fuel threw him 10 feet according to the bmfa accident report.
make sure you keep the fuel and batteries in seperate compartments.

on a lighter note i like your box, its minimalistic but with plenty of room. i cringe when i see these huge 5 tonne flight boxes on truck wheels, i think some people must bring their whole workshop with them to the field!!!