Voltage Indicator

[crutschow]

Never put voltage on a Neon.

I second that.
When I was a kid and knew just enough about electricity to be dangerous, I connected a small neon bulb directly across the 120Vac mains.
There was a bright flash of light and then nothing.
The bulb ended up blackened with the two electrodes completely loose inside the bulb. ;-)

 

[ronsimpson]

relying on potential dividers that use 100 MΩ resistances.

I have not thought about what resistance to use (100 meg), that number was just a guess. I would need to know how much load is OK on the supply and how fast the caps are to be discharged. I would not use one resistor for 1000 volts because that is a special resistor. Many resistors can do 200 volts so I would use five resistors in series.
If you are concerned about 100M resistors, then you probably don't trust high voltage meter/scope probes.
I only care about the two resistors dividing the voltage. The actual value is not important. If humidity was to effect one resistor then it would also effect the other and the "1/2" thing will still work.
At 1800V there should be about 1/2 watt in each resistor and the humidity will be a small factor. Anything below 1000V (where the current is lower) the divider could we off and it will not matter at all.
You are probably right that humidity is a factor and the boar should be slacked.