Step 3: Cut Inside Pannels
Take one of the 9" x 14" plywood pieces and mark it up as shown in the first photo below. Now Drill out the both ends of the slots using a 3/8" bit as shown in the second photo. Finally use the reciprocating saw to cut out both slots as shown in the third photo. When cutting the slots make sure you cut just outside the lines because they need to accommodate the 9 1/2" x 44 5/8" and 11" x 44 5/8" pieces as shown in the fourth photo. Once you have the slots cut out test fit the 9 1/2" x 44 5/8" and 11" x 44 5/8" pieces as shown in the photo. Each board should be able to pass all the way through their respective slot.
IMPORTANT NOTE: The two remaining 9" x 14" plywood pieces will be used for the ends and do not get cut in the next step so set them aside.
Use the board you just cut out as a pattern and mark up 7 of the 9" x 14" plywood pieces as shown in the final photo. Cut these 7 pieces out using the same method you used to cut the first one. Remember to test fit each piece as instructed earlier before moving on.