Hicky
Guru
This is canvas/poly cotton - I do have some waterproofing spray (proper stuff - used on our canvas/polycotton sun awning) - so should I take some with me on the first camp, just in-case ? Unfortunately, first camp in it will be the first time we really get it out - it's too big for our garden.
Nope, it should never need it. There's loads of vids on weathering polycotton, essentially it needs a soaking to close threads up.....you might not get any water/mist through it the first time if you're lucky and that's it done. My Dutch pyramid was really heavy tenkate cotton and needed two soaking/drying sessions, after that I just used it and thoroughly dried it out after each use(which needs doing or it will rot).....oh check the guylines when camping as they'll need slight adjustment when you have inclement weather and the cotton tightens up.
As I said there's plenty of youtube info out there.