TJ97tim,
For what it is worth, I made a 10x10 diamond out of some cotton sheet material from Joann's. I wanted a lightweight shelter that I could trek with. Anyway, I treated it with Nikwax for cotton to stay away from the stiffness and fire hazard of the traditional recipes. For two years now, it has kept me dry in several downpour weekends. As a matter of maintenance I plan to wash and retreat it in the spring.
I will add that the Nikwax stuff smells a lot like elmers glue. Someday I will do a test with some diluted elmers glue on scrap cotton.
Blessings, Bill