2010 Cougar, this is the first time that I've ever had to add Decor to the seams. In the pic you'll see the spider crack and that's the only one on the entire roof. I added extra around the antenna as a precaution. There's a finger print in the pic but I think that's from climbing up and down on the roof.
As for caulking going to hell in a hand basket after the first 6 months to a year, don't believe everything that you read. If you maintain your trailer properly and stay on top of things you'll have years of trouble free camping as I have had.
I just spent another 7 trouble free weeks in Alaska and if I didn't keep my TT in top shape I'm sure that I would've had a leak with the rain up there and been posting about it here.