I can understand an RMA department being a little probing. After all, there are people who take advantage of warranties and want a replacement from misuse or abuse and conveniently leave those details out (anyone who has bought a used car or fixes cars knows this, a lot of failures are not due to normal wear and tear).
That said, it's frustrating if you've honestly used the product normally and the company is giving you issues.
I've never lived in an extremely humid environment, but if a company offers a warranty in a region, it should be acclimated to work in in that environment WITHOUT climate control, barring natural disasters or unusual circumstances.
Companies I've had fantastic support experiences with have been Dell, Logitech, and Newegg. These companies went above and beyond the terms of their warranties, and I didn't have to pay a dime.
I'm sure people have had bad experiences with the above companies. I'd recommend OP to talk to someone else on the eVGA team, as they have a reputation for good support so someone else is bound to help him better.