Step 2: Core exercise...
Take one box and peel away at the seam to get a long flat sheet of cardboard.
Cut is so that you have a strip of cardboard 15 inches high along the entire length. You can vary this depending if you want your seat higher or lower.
Start creasing the cardboard so that you can roll it up into a tube. The open inside diameter should be about 4 inches.
The corrugations should be running perpendicular to the length of the strip.
The closer you make the creases, the easier it is to get a better formed tube.
Apply glue to one surface and start rolling it tightly like a sushi roll.
It helps to staple/tape the start of the inside roll so that it doesn't spring out.
Staple/tape the roll to keep its shape and let dry.
You should end up with a nice heavy duty cardboard pipe. Mine turned out like a cast iron 4" drainage pipe.