You could make a simple mold and cast the whole thing in a black potting epoxy or polyester resin. What are the dimensions of the routs? You can buy blank 5 string shells that are 4.062" long, i.e. halfway between the Fender "extended" neck and bridge covers which are 3.95 and 4.125 respectively. There are also 4.5" long covers for sale somewhere because lots of other makers seem to have no problem locating them.