odds are its not the camera's fault, its the temp swings and condensation building on the lens, pretty much all camera's can have this issue when environmental things cause fog/condensation and such
you wills ee this on your car windshield;as temps change too and moisture levels change in the air!
you can TRY treating the len's with things like Parkers anti fog, and or even just shampoo, or what ever you wish
it will help some, but the placement of your camera in a swamp is the issue IMO
I have run cam's for 20+ yrs, being by water and humidity, tempo swings and such will play havoc on your camera's and ruin many in short order
dampness and water, and electronic's never play well together for long!
you can TRY building a box and or a larger roof like and placing camera in/under it, to help curb some of the fogging too, but will get white wash when taking IR pictures!
its just part of life when you have glass and plastic like len's and you have a lot of moisture near by, as temps swing /and air pressure changes, fog will happen and build on len's!
I wouldn;t be blaming the camera's for this!
if they work in dry conditions, then its the moisture that is causing the issue's
unless you can get rid of the moisture, your going to have same issue with other camera's if placed in same spots!