Depending on the brand of camera, some have a rubber plug in the bottom (2009 model Bushnell Trophy trail camera). I find this a soft, poor fitting plug. I put a strip of masking tape over the hole on the inside of the camera. Another forum mentioned raid (in the black can). I don't know if this is a spray, powder or paste. Raid cans come with different chemicals listing on the can what each type is designed for. Each type has a different color on the can.
Check any rubber "O" ring around the door etc. to make sure it is still in the proper groove or parts are not missing. Good luck.