The picture below shows generally how my swamp cooler works. Not shown is the 12v fountain pump that sits at the bottom, amd pumps water through the radiator first, then from the radiator a hose runs to the top of the cooler pad and holes in it to soak the cooler pad.
Mine is built into a tall rectangular kitchen garbage can, so that I can place it on the passenger seat, and the outside air in/out vents are near the top so I can leave the passenger window down 3-4 inches. I have a house gutter guard that I cut to fit, and roll my window up to lock it into place. It has a screen in it, so it keeps out bugs, most would be thieves, and most rain.
This design is an “indirect swamp cooler”, and it won’t add any moisture to your indoor air, and it will actually dehumidify your indoor air as the moisture in the air condenses on the radiator and falls into the water reservoir.
I’m using a +/- 3" computer fan on the outside air side, and a 10" O2-Cool fan from walmart (<$20) on the inside air side.
"Stay home, stay safe, and remember social distancing." ~ Van_Dweller