Gather these parts first
Flip one of the door opening plates up side down and slide the end walls onto it as shown above
Slide the other door opening plate on the other side of the end walls with both sides showing the detail facing out
Glue the base plate onto the bottom of the assembly so far
Flip it over and glue the rim onto the top
Now gather the parts above to make the removable door
Glue the two door surface plates back to back with the detail showing. Make sure that they are lined up as closely as possible
Apply glue and slide the tall "U" shaped bars down into the slot on your door. Ensure that the door and the bars flush on top and bottom.
Now glue the top plate onto the door
Now gather all of the parts above on your parts sheet
Glue the textured ribs into the 4 slots on both sides of the door.
Glue the central gun piece into the middle of the ribs from the previous step
Now your door can drop into the frame
Prime with Rust-o-leum Profesional Enamel flat black and paint as normal with hobby paints.