I just finished up redoing the upholstery on the Laurentian tonight. The final piece was the rear seat bottom. Other than finding the build sheet and a date tag, I also found this:
Looks like perhaps a cigarette was tossed out the window and came back in and landed under the rear seat. I bet it smoldered out on it's own. Good thing or I'd still be looking for a solid 69 Canadian Poncho! Todd