If they stay in the same climate, and are protected from direct rain, it should be no problem. I had a 20D and 5D on two Amazon trips - much more humidity than Dominica - and it was not a problem. What can be a problem in the tropics is coming out of air conditioning and then dealing with instant condensation. Takes about 15 minutes to clear.
I carried several gallon size Ziplock bags and used them for "raincoats." They are also handy for packing underwear etc.