So bumping this old thread here with an update. The non sag Alpha sealant has not really held up that well along the top of the rail.
We are getting ready to head out soon for another month long trip and I see there are some cracks showing in it. I assume that the combination of it being applied so thin and the roof expanding/contracting is not a good formula.
Luckily I only applied about 5 or 10 feet of it, instead of the entire 60 plus length of both sides. I guess that leaves me with either trying to put it on thicker or using something different.
I reached out to Geocel and they say the 2300 MHRV shouldnt harm the roof, but it wont stick to EDPM. They were unable to provide any information about it sticking to TPO though.
This seems like a common area that would need touched up every so often. I am a little surprised that nobody claims they have a great product for it?