Making your own PVC boat cover will save you a bit of money and, with proper care, give you a boat cover that will work well for more than a single season. You'll need to have some skill with a needle and thread, but since you'll use the boat itself as the pattern for making the cover, your cover will fit well and keep weather vermin out of your boat. During the off season, you'll also be able to leave the cover loose enough at the bow and stern to allow good air circulation, preventing mould and mildew growth in your stored boat.
Lay the sheet of PVC over the boat. Use duct tape to tape one side of the PVC to the side of the boat. Pull the other side of the PVC tight and tape it.
Tape the PVC to the transom (the back wall) of the boat. Don't pull it tight; you want to be able to lift it and allow air circulation under the cover while the boat is in storage, to prevent mould and mildew in the boat.
Go forward and tape the PVC to the front of the boat, without pulling the PVC tight. feel along the PVC on the sides to find the male posts attached to the boat that will connect to the female part of the snaps in the PVC and mark the PVC with those locations. Repeat this process for the bow and stern of the boat.
Trim the PVC 1 inch larger than the pattern formed by the snap locations using scissors. Turn 1/2 inch of the PVC under and hem it with small needle and sailmaker's synthetic thread. The snap locations should now be in the part of the PVC that was hemmed.
Set the female part of the snaps into the PVC at the locations you marked initially, following the instructions for the particular kind of snap.
Always mount the posts onto the top of the rails of your boat before you begin to make the cover.
This project will involve sewing. Appropriate caution is advised.