Yep, I've seen it. That stuff is more like a "putty" than anything else. On mine when it gets hotter the more "gooey" it gets. I just stab, smear, and push it back into the seams the first year I owned mine. After about a year it all dried up. I don't like covers so I never had it smear everywhere like you did.
2015 Forest River EVO 2850
2012 Dodge Ram 2500 6.7 Cummins
Yamaha 2k x 2 with parallel cable
EMS 30 PI portable w/ Edison plug
Nights Camped (2016-13) (2015-13)