JonD,
Don't earth one side of your track.. DCC is a balanced system, and will not like it..
If you get a nearby lightning strike, there will be many kV per metre field-strength, and if one 'leg' (track) is earthed with respect to the other there will be a larger potential (voltage) difference between the two rails. - If both are floating, then they should both have the same induced voltage (near enough) in them. It is where this voltage finds to go that does the damage.
Ground BOTH, or neither, but a big gap and unplugging the CS is your safest bet.
Dampness is a real problem if you leave things powered-up..
Damp and DC, and you have a battery / electro-plating system.. All the copper will migrate from anode to cathode.
If the 'dampness' is slightly acidic, then the effect is enhanced.
When looking after computer newsrooms.. If a keyboard had coffee (or worse Coke) split in it, and was left connected. The small currents flowing would mean large areas of printed circuit would 'disappear' if it was left a day, or so, before we were told about it!