That's a really good question! It's a shame it even had to happen--but, it is what it is. I imagine there's several different types of sealant that could be used here. I think I would buy some clear silastic (tube) and put a couple of beads right down the center if the tear. I'd then use about 1" wide metal or plastic spatula to spread out/smooth the beads into the material. This should, after it dries, give you a good strong, flexible repair that should last for years.
Days camping (2015)----88 days
Days camping (2016) ---110 days
2016 Wildcat MAXX 28RKX (33' TT), 2007 13' Scamp
2015 Ram Laramie Hemi
30 years RV'ing
12 different RV's