The whole reason for using a transformer in a project like this is to provide isolation between the AC line and the heater side and to reduce the voltage on the load side to minimize shock hazard. As you have drawn it, you have the load side connected to the line side, so why bother with the transformer(s)?
If you dont care about shock hazard, then do what the previous poster suggested; namely eliminate the transformers, and connect the resistors in series, and power them directly from the 120VAC line.
Why don't you just discard the resistors, and wire up a single 120V lamp socket. Then everything is insulated, and you can pick an appropriate Wattage to heat your box by just screwing in a different lamp; anywhere from 10W to 150W.