Step 2: Build The Box
The first thing to do is to remove the staples form the boards. I have no idea why, but just about every board had staples in. They come out easily as Cedar is pretty soft wood.
The base is built from 3 of the 8" wide by 6ft long boards. The boards are joined together using pocket hole joinery. This is a quick way to make really strong joints.
On one edge of 6ft x 8" board, set the Kreg Jig for 3/4" and make a pocket at 8 inch intervals. Then slide a second board next to the first and use a clamp to align the left edge and keep the boards together. Set the torque adjustment on the screw driver to prevent stripping the screw out. You can practice on a piece of scrap to get the torque setting right. Cedar is very soft so keep the torque low. Screw in the first 1-1/4" exterior self tapping screw.
Work your way down the board until you have all the 1-1/4" exterior self tapping screws in.
Now make pocket holes on the 3rd 6ftx8" board and screw to the first 2 boards so that you have a base 3 boards wide by 6ft long. All the boards are aligned on the left edge. If the wood is not all exactly 6ft long, the right end will be a bit raggedy. If this is too extreme, you can use a hand held circular saw to trim the far end flush. In my case the boards were all +/- 1/8 inch so I let them be.
Now it's time to do the long vertical sides. Make pocket holes every 8 inches along one edge of each of the two 6ft by 8" side boards. It is useful to clamp the side board to the base panel to keep it properly aligned while you screw the side to the base. Make sure you keep the left edges aligned with the base.
The 8" boards are not exactly 8" wide so use a tape measure to measure the inside distance between the 2 side boards. You should have 2 off-cuts from the original 8" boards that you can use as the end boards. They will need to be cut down on the table saw to match your inner measurement. In my case, the end boards needed to be cut to 20".
Do not cross cut the boards on a table saw with the fence in place. This is very dangerous. Measure the cut length using the fence and then move the fence out of the way before making the cut. Alternately, you can insert a 0.75" thick piece of wood between the edge of the end board and the fence, measure up and then slide the 0.75" piece of wood out of the way so that the edge of your board clears the fence. If you cross cut with the fence in place the board can get wedged leading to damage of the saw, the board and most importantly yourself.