Remove the screen pack from the upper case.
Using the same methods as used in the upper case; measure and cut out a plywood panel to fit into the lower case.
Mark out areas on the wood panel where the speakers will go. Glue wood supports onto the back of the panel to hold the speakers after checking the speakers fit correctly into the holes.
Cut some metal mesh to fit into the holes over the speakers to help protect them.
Near the base at the back of the lower case drill a hole into which will fit a DC socket. At the front drill a similar hole for a headphones socket.
Measure out the dimensions of the panel mount USB socket, find a suitable space on the wood panel and mark it up for drilling & cutting. Use counter-sunk screws to hold the socket in place.
Measure the position of the battery pack inside the lower case. On the underside of the wood panel, glue guides which will hold the battery pack securely when the wood panel is in the lower case.
Using the template from the Punnet Case
cut out a cardboard template and glue it to a wooden plate. Leave enough room around the edge to attach brackets to hold the Raspberry Pi.
Measure around the edge of the USB hub adding and extra 5mm around the sides, create a plywood board. Cut a cardboard template which matches the hub's footprint. Glue the template to the plywood board and secure it tightly.
Measure the +5v LDO and cut out a matching shape from a passive heat-sink. Use some thermal glue and cement the LDO to the heat-sink. Make sure the correct pick-ups have already been soldered on. Mount the LDO onto the USB hub.
On the underside of the wood panel find a spare area to mount the GPS dongle. Position the dongle so the GPS antenna will be facing upwards when the wood panel is in the lower case. Remember to leave a cut-out where the cable can go.