As your experience shows, a tropical environment is a difficult challenge for electrostatic speakers, as for any high voltage apparatus, even including the mains power grid.
Right off the bat, because of this, I have to say that I'm sorry that we can't warranty our speakers for the usual five years in the tropics. That said, however, there are a number of attributes that should make them serve well for that long between services, which I believe is longer than QUAD speakers will keep working:
Lower operating voltages -- because cone woofers handle the bass frequencies, the bias voltage is only about 2000 Volts instead of 6000 Volts, and the drive voltages are commensurate
Protective barrier membrane over the working membranes
High voltage electrical nodes coated with an insulating material
Hardware that won’t corrode (stainless steel, brass, copper, zinc, and polymer -- no steel)
Panels are inherently immune to trouble from repeated expansion/contraction caused by wide temperature variations
Speakers that are destined for the topics have anti-fungal treatment of grill cloth and wood
I am considering adding a feature for tropical service that consists of a small drawer in the back of the cabinet that holds dessiccant packets that can be replaced or baked dry on a regular basis. If frequently enough attended to, this should extend the service indefinitely. There would be a modest extra charge.
There are pairs in Singapore and Hong Kong, but these might be in homes that are always air conditioned, so I can't necessarily hold these up as examples for you.
I have never been to Bombay, or anywhere in South Asia, although I’d like to visit. I think that if five year or longer reliability could be truly proven for our speakers in open-window Bombay, that would be notable. For this reason, I can offer you free shipping and a discount for your bravery if you order a pair.