Now you need to use your tape and tape all the sides you just cut to the coffin bottom. Be sure to tape to the bottom, and tape the sides that touch at the ends together. This should hold pretty strong. Now, if you want to have a coffin with a door that swings on one of the longer sides, do what im about to say, if you want to hte cover to just kinda be removable, skip to the next green block.
Ok, so basically place your cover piece onto the coffin where it should be. Now take your tape and go down one of the longer sides on the cover. Attach it to the wall that side touches. Tada, a door that opens and closes.