Best I can think of is to find a skateboard shop and post that you want a dead board, no trucks, state the state of grunge you want and attach it to a skeleton frame type rack. I would suggest you attach it to a large Wald paperboy frame and get the maximum utility from such a unique arrangement.
I would suggest adding eyelets instead of cutting slots for bungees and ropes if you can anchor them on the frame not the board. If it delaminates it will weaken and your tie points could be compromised.
Treating your rack for weather durability is recommended also.
Do post pictures if you go through with this project? It sounds like a great and whimsical idea and we would love to see the results!