I too have seen St Elmo's fire a few times in a C130.
The last time was the most spectacular. We were flying somewhere over North Western Pakistan up at 330 avoiding thunderstorms. We had just passed a really large cell and were out of the cloud.
Initially, on the windows just by the wipers, green snakes of light dancing up the screen. I thought the window had cracked as they looked like they were arcing.
Then the colour changed from green to blue to magenta, and the whole probe, all the windows and the leading edges of the wings were alight with little spikes of lightening.
The noise became quite deafening, sparking, the copilot was shiittiing himself and screaming and then the most beautiful sight - the probe gave off an amazing canopy like someone had just opened an umbrella of purple sparklers all radial and focused on the probe.
Wish I had my camera