Hi
I bought a pure sine wave inverter from ebay, it was not expensive but it certainly wasn't the cheapest, rated at 800W continuous 1KW surge 240V. It ran for months without a hitch in my shed. Then one day the lights didn't come on when I flicked the switch. I removed the inverter and took it into the house, went for my evening meal, when I came back I connected it to a battery and switched it on. It worked perfectly, it worked for several weeks then stopped again.
To cut a very annoying story short, the gap between the PCB and the inverter case was so small that when the humidity went up and started to condense on cold surfaces the gap was so small that the condensation was transferring to the PCB, I then found only the under side of the PCB had any solder mask or coating, so the top side of the board was covered in condensation stopping the inverter from working.
I removed the board put it in the airing cupboard overnight and sprayed the complete board with conformal coating. To me it was an annoyance to anyone without the facilities I had it could have been a disaster requiring the replacement of the inverter.
I now read all the specs for any more items I buy including the humidity rating, something I never thought of doing in the UK in the past.
Brian