People considering a 12 volt MOSFET amplifier should beware that not a single reputable transistor manufacturer is advertising a 12 volt linear RF MOSFET datasheet in this type of plastic package at power levels this high. Because of that, the ones that are working are almost certainly relabeled switch mode transistors not intended to support bias or linear operation.
All types of tricks are being used to make them function in the linear mode at the expense of reliability and durability. They include adding everything from extra resistors shunting the bias voltage across the gates to using transistors with much higher peak current ratings, hoping that will translate into some ability to sustain AB bias without failure.
That bias also increases the operating gain of a part that struggles to maintain stability due to high inductance and the larger RF currents related to a lower operating voltage producing hundreds of watts. They run hotter than the old bipolar transistors too.
If you understand this ahead of time and don't choose a model that will have to be pushed in order to reach your goal, you'll probably be happy with the cost and performance. Beat it up a little like you could with more rugged transistors and expect disappointment.