How to pack your art for shipping can be found on the Saatchi website. However now that I have done it couple times I thought I would add these pic's to clarify the process.
The painting is 24" x 60" x 1.5' so the shipping crate translates into 30" x 66" x 6"
1/2 inch plywood and 1" x 6" lumber.
Next line the crate with 1/2" foam board.
Then wrap the painting in archival acid free paper. Then wrap in heavy plastic. Then wrap in bubble-wrap. Then use heavy cardboard corner protectors. Tape everything to secure.
OK we are on the home stretch. Pack the top with more styrofoam and screw down the top. Mark the screws so the purchaser or customs don't have too much of a struggle to open. Mark FRAGILE and DO NOT LAY FLAT. As this is how most things are broken in shipping. Cross your fingers and now have a drink. You earned it. :-)
There is a shitload of paperwork to do. I would not even attempt this without the help of Saatchi Art. They take 30 to 45% on a sale but when you have to cross International borders you will need the help of a broker or Saatchi. Best of Luck. G