My Zinger's rubber roof extends under the front cap and under the front skin by about a foot. No standards.
I too would not use anymore sealants and seal it right with Eternabond. The stuff is amazing and will outlast the trailer.
I searched and searched for the source of a small leak on my trailer. Only after I sealed everything with Eternabond did it stop.
2012 Crossroads Zinger ZT26BH
2012 Ford F350 Lariat 4x4 6.7L PSD SRW
11,500 GVWR, 3522 lbs of payload