Electronic – ZVS induction heater MOSFET failure

You can make it with one MOSFET (paralleling them increases current capabilities), you just have to make sure you keep within it's ratings. Something like this circuit only uses a single IRFP450:

You could drive from the high side using your P-channel FETs, but I'd keep it simple and lowish power/voltage to start with.

Obviously be very careful with the high voltages ;-)

For a P-channel version, you can just swap all the polarities around from a design like this. You should end up with something like this (disclaimer, although it simulates okay, I have not tested this, so check everything carefully. The parts are not recommendations, just what LTSpice had available):

MOSFETs are sensitive to voltages exceeding their ratings.

When you switch off the device, the inductive coil is very likely to have generated an inductive back-EMF of voltage high enough to damage the MOSFETs. After all, the electrical energy stored in an inductor has to get out of somewhere - When you power off, the energy finds some path or the other to discharge itself, and resultant voltages can be considerably higher than the original voltage across the inductor.

A generic fix for inductor back-EMF woes is to apply a reversed diode across the coil, or in this case, possibly across the MOSFETs. Do not depend on the body diode of the MOSFETs to provide a discharge path, as body diodes rarely have suitable characteristics to serve as a high energy discharge path.