swampcoolers just need water, maybe 3 liters in a hot day, less if its not that hot. The air blowing through the evaporator pad is what gives the cooling effect. Its a very simple design.
picture of inside swamp cooler
To install a roof vent, after you buy the vent, line it up on the inside of the vehicle where you want to install it. By feel make sure there are no obstructions under the headliner material. You don't want to cut through wiring or roof support beams. You want to cut only through roof skin.
If you try to line it up outside, you wont be able to notice wiring support beams. I learned the hard way. The support beams are thicker metal which the jigsaw will easily cut through, but its best not to touch them.
Make sure you have all the screws needed, rv putty tape, a step drillbit (about 10 dollars at harbor freight) and a cordless jigsaw (about 30 dollars at harbor freight). The step drillbit is to make a hole large enough to get the jigsaw blade started. The jigsaw will make quick work and give you a straight cut. Make sure you have a jigsaw blade for steel, some are for wood only. There is also cordless sawsaws, don't use those, they are not for precision work, and you need to to have an accurate cut the first time.
If you got the right tools, installing a roof vent is fairly easy. I got 3 on my astrovan.
