I have the FC150 which has a single 1000w element on top, and two 250w elements wired in parallel below. The controller simply drives two mechanical relays which gate 120vac to the elements. The control board connects to the elements with standard quick-disconnect terminals which made it real convenient to eliminate the controller and run the wires out to a pair of 10A solid state relays. Does the "300" in your FC300 mean 3000w (more elements), or just indicate the additional rotisserie?
So far I have only driven the SSRs manually to get a profile of the oven's thermal behavior; top element only, bottom elements only, all elements, with trays, without, etc. It looks like "top only - with tray", along with manually opening the door for cooling, is the sweet spot
The oven controller at http://www.rocketscream.com
looks like a tidy little design and something I can emulate with parts on-hand. It uses Brett Beauregard's PID library, http://www.arduino.cc/playground/Code/PIDLibrary
, and includes a front end written in Processing.
I'm undecided whether I should spend today playing with that software and twiddling PID parameters, or just reinstall the oven's original controller and go the route I just discovered here...http://www.youtube.com/watch?v=8j0impc6ebQ
... five minutes on "Re Heat" followed by a brief "Toast". That's pretty straight forward and would assure plenty of time to get ready for tonight's New Year's Eve festivities. But then again, spending the day poking at PID loops sure has a lot of geek appeal.