FOD covers

For canvas FOD's you can use some epoxy putty like Milliput.
Put it inside intake and then shape it with a wet toothpick.A photo of the real think will help you when you shape

There are two types of covers used. The soft type, usually canvas, can be made with tissue paper. Wet it and form it over the intake. Trim and then soak it in a solution of white glue and water. Form it arount the intake again and let it dry. Trim to final fit and spray more solution on the cover and let it dry again.

The hard type, or intake plug, was usually made of hard plastic and fit into the intake. The way I made mine was to take thick plastic as the starting base. I glued the ribs to it to form it into the shape of the plug used by that aircraft. I used that as a master to vacuform the plugs. You may have to make left and right masters depending on the type of aircraft.