So today was one of those "Sit & Think" times. I measured & cut the back panel, notching out slots at the top for the trunk hinge supports and a big rectangle for the battery box and quickly remembered why there's a lap joint in that bulkhead divider. It simply won't fit full width & height. I finally decided that I'll cut the back panel in half vertically, upholster them and mount them with velcro, then make a padded center piece, wide at the top and arced to a narrow base in the middle, to cover the joint. By the time I got that decided it was getting late in the day, so I'll cut the panel tomorrow, then get the sides done in wood and make everything fit.