Cardboard would work for me. Given that I have a sawmill, I've also thought about sawing out some nice Eastern Red Cedar, and either building my own, or, having the Amish build one for me. Supposedly the Amish around here make caskets exclusively out of red cedar.
I did saw out some red cedar for a customer one time who was building his own casket. Approx 6'-6" tall. Claimed that he had a friend who had to have his legs broken to fit in a standard casket so as not to have the family wait for a special order, extra length. Customer decided he would just build his own to fit, and not have his family have to deal with any potential logistical issues. Not sure if the story was true. But his cash was green, so, I sawed out what he wanted...
