Wow! That doesn't look good. I'm so sorry for your problem. I hope that your dealer and Keystone step up and do the right thing and get you going quickly.
A word to others; I was at the CW yard about 2 weeks ago looking at new Montana's - I didn't have a salesman. We looked at a few and were walking along the fronts of them checking them out. I was maybe 10 yards in front of them looking at the fronts and happened to look up at the rooflines. One of them looked VERY much like this must look from the ground. The roofline didn't look exactly right and it looked like all the sealant (or something) was just sort of sticking up in bits and chunks all across the front along the seam. Didn't look right to me so got a guy and told him and he said they would look at it.
I was back in today but completely forgot to check on it (checking on mine seems to take up most of my time
). If they just sealed that thing after it had been sitting no telling how long like that, and it was as bad as this photo, someone is going to get a real "deal". My take away from that is; when looking at a trailer, even a brand new, upper line model, be sure and check the roof seams closely. Finding something like that on a new trailer would be gut wrenching as I know it is to the OP.