Fight inrush current with PTC, good go or not?
I cannot envision how a PTC can reduce inrush on a converter. The inrush IS the capacitor charging current, so it is virtually instantaneous. It is PRECISELY the first few microseconds of time where you NEED the series resistance to limit the current. That's why NTC thermistors are used: high resistance when cold, lower when hot. If you don't like the residual low resistance afterward, you can bypass it with a lower resistance device (switch) AFTER the caps are fully charged, so the thermistor can immediately cool down and return to the high ohm state. But if you are going to do that, just use a regular resistor. An NTC thermistor is used because you DON'T want the cost of adding that other bypass device, but can live with the small amount of resistance is presents in the circuit. 

A PTC thermistor would do nothing in the first moments, THEN increase resistance, which is totally pointless in avoiding inrush.