You must be confused with the method of rating power mosfets: "200W@25C case temperature", the rating assigned, is just an extrapolated value, and applies if the user somehow managed to hold the metal base temperature at 25C. At 65C cooler temperature, the centre of the mosfet's base will be even hotter, may be 85C. It needs a correctly attached thermocouple to check this. And at this 85C base, the chip inside will reach 150C for a power dissipation of just 100W!, not 200.That it survived for a time at 200W demonstrates a margin of performance not meant to be exploited by the user.
Though you might get a 400W@25C mosfet in the same case, it is best not to push temperatures so far. I would use THREE IRF250's in parallel, and hold their bases at 65C by the heat sink. Obviously, the mosfet's should attach to the heat sink directly i.e., without any shims or spacers.