PWM would work fine with the solid state relays, but your PWM cycle should probably be at least a 20 second cycle, not in the Hz range. The PWM frequency depends on how close you want to hold the temperature, the oven inertia, and a few other things you need to consider. Using the SSR with zero cross you do not have to worry about phase angle etc when it is on or off for several seconds or more. This also eliminates EMI/RFI noise. Since you are using upto 10A give yourself some cushion and use a 25 or lager SS relay they do not cost that much more.