As several DIYers out there, I’m a big fan of the Russian teflon FT-3 capacitors in my preamps. I normally use the 220nF/600V ones as have plenty of them in stock. These are superb in my view, however mounting them is a royal pain in the back. I used turrets for some time, but I ended up building a simple PCB which has a cutout to fit the FT3, solder it firmly on big copper pads and then solder the connections from the PCB. Also added a bias resistor (either for charging/discharging the cap or for fixed bias) which is connected to a GND terminal. This GND terminal could be used for the negative fixed bias if required. The PCB can be stacked very easily as has 4 M3 hex standoffs:
