Step 1: 3D Print Coffin

3D print the coffin in black. I used an Ultimaker 2+ with a fast print (Cura) in black PLA. If you do not have access to a 3D printer via your library, school, maker space, etc, you can use a 3D printing service like Shapeways.

I modified the dimensions of this design. I did not print the lid. I have attached the OpenSCAD file in case you want to modify the dimensions.

Step 2: Create Lining Pattern

Trace the outside of the coffin on paper. Carefully trim the bottom edge and the bottom left/right edges to fit the inner dimensions of the coffin. Push the pattern down into the base of the coffin and align the bottom and bottom left/right edges. Use your fingernail to fold the top and top left/right edges at a right angle to get the right dimensions.

To create the pattern for the other inside surfaces, I measured the inside dimensions of the coffin and created patterns in Inkscape. That file is attached for you to print and cut out.

Step 3: Cut Out Lining

Pin the patterns to the red felt and cut them out. Be sure to keep track of which piece goes with which edge.

Step 4: Glue Lining

First, glue the base down. Then start applying the felt panels to the inside edge. You will need to trim them down slightly - otherwise they will overlap. Apply one panel at a time and trim accordingly. For the long panels, only apply glue to part of the coffin, get it lined up, then glue down the rest.