[Amps] 2 meter Amp output cap voltage levels

[N7EME]

I'm finalizing a GS31B 2 meter Amp and have a question concerning the 
breakdown voltage capability
of the output tuning and coupling capacitors. The matching network is 
Cap coupled using a 1000pF 5KV
coupling cap. The plate voltage is 3300VDC. Power output is estimated to 
be around 1200-1300Watts.
Now I know that having the 1000pF cap reduces the breakdown voltage 
requirement of the tuning and
coupling caps, but what do they need to be as a minimum plus say a 25% 
safety factor?

Thanks
Jerry - N7EME