Storm windows can reduce your heat loss through the windows by 25% to 50%. Storm windows should have weatherstripping at all moveable joints; be made of strong, durable materials; and have interlocking or overlapping joints. Low-e storm windows save even more energy.
Toenailing styles can vary. Some pros like to drive three or four nails into a stud, toenailing from both sides at about a 30-degree angle. The job is easier if you first drive a holding nail on one side of the stud, then drive two nails on the opposite side. Remove the holding nail, then toenail the second side. You can also make up a 2×4 spacer to place between the studs.