I bought mine about two years ago and after about a year the tarp cover started to crack and open slits along the areas where the tarp rested on the frame. I put the portable garage up close to the house and under a large tree so it was fairly well shaded most of the time.
I bought a second tarp cover a year ago when the leaks got pretty bad and it, too, lasted about a year. I never worked on the TTT inside the "big top," just stored it in there when I wasn't working on it.
I am currently shopping around for a metal carport to store my TTT under and to work under during inclement weather. Those come with a 20 year warranty. If the sun eats through that, I'm moving north.
Just some food for thought in the hope of saving someone $300 and a whole lot of headaches.

Brian