Unex has excellent quality industrial temp 5.8Ghz card with low EVM (clean) TX output at 100mW. You could use that with a reliable Mikrotik board.
Use a roomy outdoor enclosure suitable for tropical climate to put everything inside. Add good quality surge protection for Ethernet/PoE and bond antenna/RF ground to Ethernet ground and metal enclosure body.
Thanks for your advices and help. There is a high probability that I will deploy this link and it would be on the suggested frequency - 5.8 GHz. Just need to re-visit those places and talk to the community again - Will post results if project takes place.