I ordered a lighter weight canvas for the tarp, #12. I have used both #'s 10 and 12 on canoes, 10 is tougher but is too heavy, as a tarp #12 will be fine. I wanted Sunforger canvas with it's tighter weave but could only find it in 60" width, I needed 72" to get a decent overhang on the wall tent, and only one seam at the ridge. The canvas I ordered is white, which should let more light into the tent during those dark overcast fall days.
Not sure if I'll go with a beeswax concoction or a chemical waterproofing like Canvak.