From 12V to 325v - 400v DC DC converter
This is a fairly trivial design as far as power supply designs go, if you know how and no more dangerous to use,  than a neon indicator tube.  Suitable skill and care is still needed,

I strongly suggest you follow the Manufacturer's advice in the datasheet.  

Frankly your incorrect assumptions, so far tell me your best bet is the miniature supply board and cables from the Mfg.