DIY RV Swamp Cooler

Cut a 20-by-12-inch hole into the side of a lidded heavy-duty 45-gallon trash can; use a utility knife for a plastic can, and a jigsaw for a metal can.

Fix a 22-by-14-inch evaporative pad to the inside of the hole. Drill small holes around the periphery of the hole at eight-inch intervals and thread nylon cord through both the can and the pad, "sewing" the pad to the hole's rim, or use duct tape for a speedier but less permanent attachment. A piece of bug-screen fitted to the outside of the hole will exclude insects from the inside of the can.

Obtain a length of insulated concertina trunking of the type used to vent clothes dryers, cut to comfortably reach between the intended location of the swamp cooler and the inlet port of the RV. Use the same cutting tool as before to make a much smaller hole in the opposite side of the can, sized to accept the duct. This hole will vent treated air from the DIY RV swamp cooler, via the ductwork, to the location to be cooled. Slip the duct two inches into the new hole, then secure it in place either with nylon thread or duct tape.

Attach a car radiator fan to the inside of the can over the exit hole to the ductwork. Use the most powerful unit that your budget and personal tolerance for noise can support. Fix the fan to the can using "U"-bolts passed through its mounting flanges, with washers and nuts drawn tight to the outside. Larger fans will require the use of a reducing hub, again readily available from home improvement warehouses, to step down the diameter of the fan to that of the duct.

Use eight-gauge wire to connect a fully charged deep cycle marine or RV coach battery to the terminals of the fan, or connect it to the 12-volt coach circuit of the RV via an inline switch. Reverse the connections if the fan initially sucks the air instead of blowing it.

Soak the evaporative pad and put the trash can lid in place. Within seconds, cooled forced air will be emitted from the open end of the duct.