The two main reasons for designing and installing a pool pump cover on an outdoor pump are to protect the pump motor from moisture and to dampen the noise when the pump is operating. Pool pump motors are air-cooled and ventilated to allow the pump fan to draw in cool air and circulate it around the windings so the motor doesn't overheat while operating. Here's a simple way to solve both the moisture and noise problems.
Protect the motor from rain, hosing and accidental water spills around the pump equipment by cutting a 14-inch by 14-inch square of neoprene, a closed cell foam which is flexible, durable and waterproof. This is a large enough piece to cover the entire length of the motor and the electrical conduit connection at the rear of the motor while still allowing access to the pump's hair and lint basket under the pump lid at the front.
Find the center of the neoprene square and mark two parallel lines 2 1/2 inch out from each side of the center. This gives you two marks five inches apart. Cut a 1/2 inch slit through each parallel line.
Turn the pump off and lay the foam square over the top of the motor so each slit is over one side of the motor. The front end of the square should rest up against the back of the outflow pipe on the pump with the rear end of the square hanging over the motor's back end and conduit connection. If the square is a bit too big for your motor, trim it to a smaller size.
Pass the reusable cable tie under the motor and insert the ratcheted (toothed) end up through one slit and the locking end up through the other. If you can't find a cable tie long enough to encircle the motor and meet above the neoprene cover, you can join 2 cable ties together for added length.
Lock the cable tie at the top of the motor and cinch it down to tighten the neoprene cover over the motor. The lower edges of the neoprene cover should flare out a bit, forming a kind of "tent" over the entire motor. This flaring is important because you want to allow enough air space around the lower half of the motor where the air vents are located so it can still pull in enough cool air to avoid overheating during operation. The reusable cable tie allows you to remove the cover easily to service the motor.
Dampen pump noise using a small rectangle of neoprene. Most of the noise from a properly operating pool pump comes from vibration. Pool pumps usually sit on a concrete pad. The hard surface of the pump foot against the hard surface of the pad can sometimes produce an annoyingly noisy situation. You can stop this noise by lifting the pump up about 3/8 of an inch and then sliding the neoprene rectangle under the foot. This will ensure the two hard surfaces are no longer making contact.