Bill,
I have the Tracker TV-18 and I bought the cover from Tracker and it just came in last night. I was really impressed with the quality of the material, construction and custom fit to the boat. There were also plenty of straps, 6 per side I think. I'm sure that the same quality (if not more) would be put into a Nitro cover.
Like I said, I just got it last night. I'm someone here has had one longer and can give us both some input on the longevity of the covers.
Marke