With the wood work done on the battery box then next step was the styrene. I started by cutting a piece that was the exact width for the end but a little longer then necessary.
Next I glued one end of the piece to the wood frame with epoxy and held it in place with clamps and tape.
Once the glue was dry I wrapped the piece around the rest of the way to determine the final length and made the cut. With the piece the correct length I glues it the rest of the way around with epoxy and again held it in place with clamps and tape. You can see here why I added a stiffener block behind the edge of the luan side made, it gave the clamps something to hold against.
The final step was to put some filler in the seams and sand everything smooth.